SEI Message Dependency Simplification In Video Coding

ABSTRACT

A video coding mechanism is disclosed. The mechanism includes encoding a coded picture into a bitstream. A current supplemental enhancement information (SEI) message that comprises a decoding unit (DU) hypothetical reference decoder (HRD) parameters present flag (du_hrd_params_present_flag) is also encoded into the bitstream. The du_hrd_params_present_flag specifies whether DU level HRD parameters are present in the bitstream. A set of bitstream conformance tests is performed on the bitstream based on the current SEI message. The bitstream is stored for communication toward a decoder.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of International ApplicationNo. PCT/US2020/051316, filed Sep. 17, 2020 by Ye-Kui Wang, and titled“SEI Message Dependency Simplification In Video Coding,” which claimsthe benefit of U.S. Provisional Patent Application No. 62/905,236 filedSep. 24, 2019 by Ye-Kui Wang, and titled “Video Coding Improvements,”which are hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure is generally related to video coding, and isspecifically related to improvements in signaling parameters to supportcoding of multi-layer bitstreams.

BACKGROUND

The amount of video data needed to depict even a relatively short videocan be substantial, which may result in difficulties when the data is tobe streamed or otherwise communicated across a communications networkwith limited bandwidth capacity. Thus, video data is generallycompressed before being communicated across modern daytelecommunications networks. The size of a video could also be an issuewhen the video is stored on a storage device because memory resourcesmay be limited. Video compression devices often use software and/orhardware at the source to code the video data prior to transmission orstorage, thereby decreasing the quantity of data needed to representdigital video images. The compressed data is then received at thedestination by a video decompression device that decodes the video data.With limited network resources and ever increasing demands of highervideo quality, improved compression and decompression techniques thatimprove compression ratio with little to no sacrifice in image qualityare desirable.

SUMMARY

In an embodiment, the disclosure includes a method implemented by adecoder, the method comprising: receiving, by a receiver of the decoder,a bitstream comprising a coded picture and a current supplementalenhancement information (SEI) message that comprises a decoding unit(DU) hypothetical reference decoder (HRD) parameters present flag(du_hrd_params_present_flag) that specifies whether DU level HRDparameters are present in the bitstream; and decoding, by a processor ofthe decoder, the coded picture to produce a decoded picture.

Video coding systems may encode a video sequence into a bitstream as aseries of coded pictures. Various parameters can also be coded tosupport decoding of the video sequence. For example, a video parameterset (VPS) may contain parameters related to the configuration of layers,sublayers, and/or output layer sets (OLSs) in the video sequence. Inaddition, the video sequence can be checked by a HRD for conformancewith standards. To support such conformance testing, the VPS and/or theSPS may contain HRD parameters. HRD related parameters may also becontained in SEI messages. A SEI message contains information that isnot needed by the decoding process in order to determine the values ofthe samples in decoded pictures. For example, the SEI messages maycontain HRD parameters that further describe the HRD process in light ofthe HRD parameters contained in the VPS. In some video coding systems,the SEI messages may contain parameters that directly reference the VPS.This dependency creates certain difficulties. For example, the VPS maybe removed from a bitstream when transmitting an OLS that contains asingle layer. This approach may be beneficial in some instances as theVPS does not contain useful information when the decoder only receivesone layer. However, omitting the VPS can prevent the SEI messages frombeing properly parsed due to the dependency on the VPS. Specifically,omitting the VPS can cause the SEI messages to return an error as thedata upon which they depend in the VPS is not received at the decoder.

The present example includes a mechanism to remove dependencies betweenthe VPS and the SEI messages. For example, a du_hrd_params_present_flagcan be coded in a current SEI message. The du_hrd_params_present_flagspecifies whether the HRD should operate on an access unit (AU) level ora DU level. Further, the current SEI message can include a DU codedpicture buffer (CPB) parameters in picture timing (PT) SEI flag(du_cpb_params_in_pic_timing_sei_flag) that specifies whether DU levelCPB removal delay parameters are present in a PT SEI message or adecoding unit information (DUI) SEI message. By including these flags inthe current SEI message, the current SEI message does not depend on theVPS. Hence, the current SEI message can be parsed even when the VPS isomitted from the bitstream. Accordingly, various errors may be avoided.As a result, the functionality of the encoder and the decoder isincreased. Further, removing the dependency between the SEI messages andthe VPS supports removal of the VPS in certain cases, which increasescoding efficiency, and hence reduces processor, memory, and/or networksignaling resource usage at both the encoder and the decoder.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the du_hrd_params_present_flag furtherspecifies whether a HRD operates at an access unit (AU) level or a DUlevel.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the du_hrd_params_present_flag is set toone when specifying that DU level HRD parameters are present and the HRDcan be operated at the AU level or the DU level, and wherein thedu_hrd_params_present_flag is set to zero when specifying that DU levelHRD parameters are not present and the HRD operates at the AU level.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the current SEI message further comprises aDU coded picture buffer (CPB) parameters in picture timing (PT) SEI flag(du_cpb_params_in_pic_timing_sei_flag) that specifies whether DU levelCPB removal delay parameters are present in a PT SEI message.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the du_cpb_params_in_pic_timing_sei_flagfurther specifies whether DU level CPB removal delay parameters arepresent in a decoding unit information (DUI) SEI message.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the du_cpb_params_in_pic_timing_sei_flag isset to one when specifying that that DU level CPB removal delayparameters are present in a PT SEI message and no DUI SEI message isavailable, and wherein the du_cpb_params_in_pic_timing_sei_flag is setto zero when specifying that DU level CPB removal delay parameters arepresent in a DUI SEI message and PT SEI messages do not include DU levelCPB removal delay parameters.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the current SEI message is a bufferingperiod (BP) SEI message, a PT SEI message, or a DUI SEI message.

In an embodiment, the disclosure includes a method implemented by anencoder, the method comprising: encoding, by a processor of the encoder,a coded picture into a bitstream; encoding into the bitstream, by theprocessor, a current SEI message that comprises adu_hrd_params_present_flag that specifies whether DU level HRDparameters are present in the bitstream; performing, by the processor, aset of bitstream conformance tests on the bitstream based on the currentSEI message; and storing, by a memory coupled to the processor, thebitstream for communication toward a decoder.

Video coding systems may encode a video sequence into a bitstream as aseries of coded pictures. Various parameters can also be coded tosupport decoding of the video sequence. For example, a VPS may containparameters related to the configuration of layers, sublayers, and/orOLSs in the video sequence. In addition, the video sequence can bechecked by a HRD for conformance with standards. To support suchconformance testing, the VPS and/or the SPS may contain HRD parameters.HRD related parameters may also be contained in SEI messages. A SEImessage contains information that is not needed by the decoding processin order to determine the values of the samples in decoded pictures. Forexample, the SEI messages may contain HRD parameters that furtherdescribe the HRD process in light of the HRD parameters contained in theVPS. In some video coding systems, the SEI messages may containparameters that directly reference the VPS. This dependency createscertain difficulties. For example, the VPS may be removed from abitstream when transmitting an OLS that contains a single layer. Thisapproach may be beneficial in some instances as the VPS does not containuseful information when the decoder only receives one layer. However,omitting the VPS can prevent the SEI messages from being properly parseddue to the dependency on the VPS. Specifically, omitting the VPS cancause the SEI messages to return an error as the data upon which theydepend in the VPS is not received at the decoder.

The present example includes a mechanism to remove dependencies betweenthe VPS and the SEI messages. For example, a du_hrd_params_present_flagcan be coded in a current SEI message. The du_hrd_params_present_flagspecifies whether the HRD should operate on an AU level or a DU level.Further, the current SEI message can include adu_cpb_params_in_pic_timing_sei_flag that specifies whether DU level CPBremoval delay parameters are present in a PT SEI message or a DUI SEImessage. By including these flags in the current SEI message, thecurrent SEI message does not depend on the VPS. Hence, the current SEImessage can be parsed even when the VPS is omitted from the bitstream.Accordingly, various errors may be avoided. As a result, thefunctionality of the encoder and the decoder is increased. Further,removing the dependency between the SEI messages and the VPS supportsremoval of the VPS in certain cases, which increases coding efficiency,and hence reduces processor, memory, and/or network signaling resourceusage at both the encoder and the decoder.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the du_hrd_params_present_flag furtherspecifies whether a HRD operates at an AU level or a DU level.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the du_hrd_params_present_flag is set toone when specifying that DU level HRD parameters are present and the HRDcan be operated at the AU level or the DU level, and wherein thedu_hrd_params_present_flag is set to zero when specifying that DU levelHRD parameters are not present and the HRD operates at the AU level.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the current SEI message further comprises adu_cpb_params_in_pic_timing_sei_flag that specifies whether DU level CPBremoval delay parameters are present in a PT SEI message.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the du_cpb_params_in_pic_timing_sei_flagfurther specifies whether DU level CPB removal delay parameters arepresent in a DUI SEI message.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the du_cpb_params_in_pic_timing_sei_flag isset to one when specifying that that DU level CPB removal delayparameters are present in a PT SEI message and no DUI SEI message isavailable, and wherein the du_cpb_params_in_pic_timing_sei_flag is setto zero when specifying that DU level CPB removal delay parameters arepresent in a DUI SEI message and PT SEI messages do not include DU levelCPB removal delay parameters.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the current SEI message is a BP SEImessage, a PT SEI message, or a DUI SEI message.

In an embodiment, the disclosure includes a video coding devicecomprising: a processor, a receiver coupled to the processor, a memorycoupled to the processor, and a transmitter coupled to the processor,wherein the processor, receiver, memory, and transmitter are configuredto perform the method of any of the preceding aspects.

In an embodiment, the disclosure includes a non-transitory computerreadable medium comprising a computer program product for use by a videocoding device, the computer program product comprising computerexecutable instructions stored on the non-transitory computer readablemedium such that when executed by a processor cause the video codingdevice to perform the method of any of the preceding aspects.

In an embodiment, the disclosure includes a decoder comprising: areceiving means for receiving a bitstream comprising a coded picture anda current SEI message that comprises a du_hrd_params_present_flag thatspecifies whether DU level HRD parameters are present in the bitstream;a decoding means for decoding the coded picture to produce a decodedpicture; and a forwarding means for forwarding the decoded picture fordisplay as part of a decoded video sequence.

Video coding systems may encode a video sequence into a bitstream as aseries of coded pictures. Various parameters can also be coded tosupport decoding of the video sequence. For example, a VPS may containparameters related to the configuration of layers, sublayers, and/orOLSs in the video sequence. In addition, the video sequence can bechecked by a HRD for conformance with standards. To support suchconformance testing, the VPS and/or the SPS may contain HRD parameters.HRD related parameters may also be contained in SEI messages. A SEImessage contains information that is not needed by the decoding processin order to determine the values of the samples in decoded pictures. Forexample, the SEI messages may contain HRD parameters that furtherdescribe the HRD process in light of the HRD parameters contained in theVPS. In some video coding systems, the SEI messages may containparameters that directly reference the VPS. This dependency createscertain difficulties. For example, the VPS may be removed from abitstream when transmitting an OLS that contains a single layer. Thisapproach may be beneficial in some instances as the VPS does not containuseful information when the decoder only receives one layer. However,omitting the VPS can prevent the SEI messages from being properly parseddue to the dependency on the VPS. Specifically, omitting the VPS cancause the SEI messages to return an error as the data upon which theydepend in the VPS is not received at the decoder.

The present example includes a mechanism to remove dependencies betweenthe VPS and the SEI messages. For example, a du_hrd_params_present_flagcan be coded in a current SEI message. The du_hrd_params_present_flagspecifies whether the HRD should operate on an AU level or a DU level.Further, the current SEI message can include adu_cpb_params_in_pic_timing_sei_flag that specifies whether DU level CPBremoval delay parameters are present in a PT SEI message or a DUI SEImessage. By including these flags in the current SEI message, thecurrent SEI message does not depend on the VPS. Hence, the current SEImessage can be parsed even when the VPS is omitted from the bitstream.Accordingly, various errors may be avoided. As a result, thefunctionality of the encoder and the decoder is increased. Further,removing the dependency between the SEI messages and the VPS supportsremoval of the VPS in certain cases, which increases coding efficiency,and hence reduces processor, memory, and/or network signaling resourceusage at both the encoder and the decoder.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the decoder is further configured toperform the method of any of the preceding aspects.

In an embodiment, the disclosure includes an encoder comprising: anencoding means for: encoding a coded picture into a bitstream; andencoding into the bitstream a current SEI message that comprises adu_hrd_params_present_flag that specifies whether DU level HRDparameters are present in the bitstream; a HRD means for performing aset of bitstream conformance tests on the bitstream based on the currentSEI message; and a storing means for storing the bitstream forcommunication toward a decoder.

Video coding systems may encode a video sequence into a bitstream as aseries of coded pictures. Various parameters can also be coded tosupport decoding of the video sequence. For example, a VPS may containparameters related to the configuration of layers, sublayers, and/orOLSs in the video sequence. In addition, the video sequence can bechecked by a HRD for conformance with standards. To support suchconformance testing, the VPS and/or the SPS may contain HRD parameters.HRD related parameters may also be contained in SEI messages. A SEImessage contains information that is not needed by the decoding processin order to determine the values of the samples in decoded pictures. Forexample, the SEI messages may contain HRD parameters that furtherdescribe the HRD process in light of the HRD parameters contained in theVPS. In some video coding systems, the SEI messages may containparameters that directly reference the VPS. This dependency createscertain difficulties. For example, the VPS may be removed from abitstream when transmitting an OLS that contains a single layer. Thisapproach may be beneficial in some instances as the VPS does not containuseful information when the decoder only receives one layer. However,omitting the VPS can prevent the SEI messages from being properly parseddue to the dependency on the VPS. Specifically, omitting the VPS cancause the SEI messages to return an error as the data upon which theydepend in the VPS is not received at the decoder.

The present example includes a mechanism to remove dependencies betweenthe VPS and the SEI messages. For example, a du_hrd_params_present_flagcan be coded in a current SEI message. The du_hrd_params_present_flagspecifies whether the HRD should operate on an AU level or a DU level.Further, the current SEI message can include adu_cpb_params_in_pic_timing_sei_flag that specifies whether DU level CPBremoval delay parameters are present in a PT SEI message or a DUI SEImessage. By including these flags in the current SEI message, thecurrent SEI message does not depend on the VPS. Hence, the current SEImessage can be parsed even when the VPS is omitted from the bitstream.Accordingly, various errors may be avoided. As a result, thefunctionality of the encoder and the decoder is increased. Further,removing the dependency between the SEI messages and the VPS supportsremoval of the VPS in certain cases, which increases coding efficiency,and hence reduces processor, memory, and/or network signaling resourceusage at both the encoder and the decoder.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the encoder is further configured toperform the method of any of the preceding aspects.

For the purpose of clarity, any one of the foregoing embodiments may becombined with any one or more of the other foregoing embodiments tocreate a new embodiment within the scope of the present disclosure.

These and other features will be more clearly understood from thefollowing detailed description taken in conjunction with theaccompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts.

FIG. 1 is a flowchart of an example method of coding a video signal.

FIG. 2 is a schematic diagram of an example coding and decoding (codec)system for video coding.

FIG. 3 is a schematic diagram illustrating an example video encoder.

FIG. 4 is a schematic diagram illustrating an example video decoder.

FIG. 5 is a schematic diagram illustrating an example hypotheticalreference decoder (HRD).

FIG. 6 is a schematic diagram illustrating an example multi-layer videosequence.

FIG. 7 is a schematic diagram illustrating an example bitstream.

FIG. 8 is a schematic diagram of an example video coding device.

FIG. 9 is a flowchart of an example method of encoding a video sequenceinto a bitstream by employing a supplemental enhancement information(SEI) message that may not depend on a video parameter set (VPS).

FIG. 10 is a flowchart of an example method of decoding a video sequencefrom a bitstream that employs a SEI message that may not depend on aVPS.

FIG. 11 is a schematic diagram of an example system for coding a videosequence using a bitstream that employs a SEI message that may notdepend on a VPS.

DETAILED DESCRIPTION

It should be understood at the outset that although an illustrativeimplementation of one or more embodiments are provided below, thedisclosed systems and/or methods may be implemented using any number oftechniques, whether currently known or in existence. The disclosureshould in no way be limited to the illustrative implementations,drawings, and techniques illustrated below, including the exemplarydesigns and implementations illustrated and described herein, but may bemodified within the scope of the appended claims along with their fullscope of equivalents.

The following terms are defined as follows unless used in a contrarycontext herein. Specifically, the following definitions are intended toprovide additional clarity to the present disclosure. However, terms maybe described differently in different contexts. Accordingly, thefollowing definitions should be considered as a supplement and shouldnot be considered to limit any other definitions of descriptionsprovided for such terms herein.

A bitstream is a sequence of bits including video data that iscompressed for transmission between an encoder and a decoder. An encoderis a device that is configured to employ encoding processes to compressvideo data into a bitstream. A decoder is a device that is configured toemploy decoding processes to reconstruct video data from a bitstream fordisplay. A picture is an array of luma samples and/or an array of chromasamples that create a frame or a field thereof. A slice is an integernumber of complete tiles or an integer number of consecutive completecoding tree unit (CTU) rows (e.g., within a tile) of a picture that areexclusively contained in a single network abstraction layer (NAL) unit.A picture that is being encoded or decoded can be referred to as acurrent picture for clarity of discussion. A coded picture is a codedrepresentation of a picture comprising video coding layer (VCL) NALunits with a particular value of NAL unit header layer identifier(nuh_layer_id) within an access unit (AU) and containing all coding treeunits (CTUs) of the picture. A decoded picture is a picture produced byapplying a decoding process to a coded picture.

An AU is a set of coded pictures that are included in different layersand are associated with the same time for output from a decoded picturebuffer (DPB). A decoding unit (DU) is an AU or a subset of an AUincluding one or more VCL NAL units in an AU and associated non-VCL NALunits. A NAL unit is a syntax structure containing data in the form of aRaw Byte Sequence Payload (RBSP), an indication of the type of data, andinterspersed as desired with emulation prevention bytes. A VCL NAL unitis a NAL unit coded to contain video data, such as a coded slice of apicture. A non-VCL NAL unit is a NAL unit that contains non-video datasuch as syntax and/or parameters that support decoding the video data,performance of conformance checking, or other operations. A layer is aset of VCL NAL units that share a specified characteristic (e.g., acommon resolution, frame rate, image size, etc.) as indicated by layerID and associated non-VCL NAL units.

A hypothetical reference decoder (HRD) is a decoder model operating onan encoder that checks the variability of bitstreams produced by anencoding process to verify conformance with specified constraints. Abitstream conformance test is a test to determine whether an encodedbitstream complies with a standard, such as Versatile Video Coding(VVC). HRD parameters are syntax elements that initialize and/or defineoperational conditions of an HRD. HRD parameters may be included insupplemental enhancement information (SEI) messages, in a sequenceparameter set (SPS), and/or in a video parameter set (VPS). A DU HRDparameters present flag (du_hrd_params_present_flag) is a syntax elementthat specifies whether DU level HRD parameters are present in thebitstream. An AU level is a description of an operation as being appliedto one or more entire AUs (e.g., applied to one or more entire groups ofpictures sharing the same output time). A DU level is a description ofan operation as being applied to one or more entire DUs (e.g., appliedto one or more pictures).

A SEI message is a syntax structure with specified semantics thatconveys information that is not needed by the decoding process in orderto determine the values of the samples in decoded pictures. A SEI NALunit is a NAL unit that contains one or more SEI messages. A specificSEI NAL unit may be referred to as a current SEI NAL unit. A bufferingperiod (BP) SEI message is a type of SEI message that contains HRDparameters for initializing an HRD to manage a coded picture buffer(CPB). A picture timing (PT) SEI message is a type of SEI message thatcontains HRD parameters for managing delivery information for AUs at theCPB and/or a decoded picture buffer (DPB). A decoding unit information(DUI) SEI message is a type of SEI message that contains HRD parametersfor managing delivery information for DUs at the CPB and/or the DPB. ADU CPB parameters in PT SEI flag (du_cpb_params_in_pic_timing_sei_flag)is a syntax element that specifies whether DU level CPB removal delayparameters are present in a PT SEI message and/or a DUI SEI message. ACPB is a first-in first-out buffer in a HRD that contains DUs indecoding order. A CPB removal delay is an amount time that one or morepictures may remain in a CPB prior to transfer to a DPB in a HRD. A VPSis a syntax structure that contains data related to the entirebitstream. A SPS is a syntax structure a syntax structure containingsyntax elements that apply to zero or more entire coded layer videosequences. A coded video sequence is a set of one or more codedpictures. A decoded video sequence is a set of one or more decodedpictures.

The following acronyms are used herein, Access Unit (AU), Coding TreeBlock (CTB), Coding Tree Unit (CTU), Coding Unit (CU), Coded Layer VideoSequence (CLVS), Coded Layer Video Sequence Start (CLVSS), Coded VideoSequence (CVS), Coded Video Sequence Start (CVSS), Joint Video ExpertsTeam (JVET), Hypothetical Reference Decoder HRD, Motion Constrained TileSet (MCTS), Maximum Transfer Unit (MTU), Network Abstraction Layer(NAL), Output Layer Set (OLS), Picture Order Count (POC), Random AccessPoint (RAP), Raw Byte Sequence Payload (RBSP), Sequence Parameter Set(SPS), Video Parameter Set (VPS), Versatile Video Coding (VVC).

Many video compression techniques can be employed to reduce the size ofvideo files with minimal loss of data. For example, video compressiontechniques can include performing spatial (e.g., intra-picture)prediction and/or temporal (e.g., inter-picture) prediction to reduce orremove data redundancy in video sequences. For block-based video coding,a video slice (e.g., a video picture or a portion of a video picture)may be partitioned into video blocks, which may also be referred to astreeblocks, coding tree blocks (CTBs), coding tree units (CTUs), codingunits (CUs), and/or coding nodes. Video blocks in an intra-coded (I)slice of a picture are coded using spatial prediction with respect toreference samples in neighboring blocks in the same picture. Videoblocks in an inter-coded unidirectional prediction (P) or bidirectionalprediction (B) slice of a picture may be coded by employing spatialprediction with respect to reference samples in neighboring blocks inthe same picture or temporal prediction with respect to referencesamples in other reference pictures. Pictures may be referred to asframes and/or images, and reference pictures may be referred to asreference frames and/or reference images. Spatial or temporal predictionresults in a predictive block representing an image block. Residual datarepresents pixel differences between the original image block and thepredictive block. Accordingly, an inter-coded block is encoded accordingto a motion vector that points to a block of reference samples formingthe predictive block and the residual data indicating the differencebetween the coded block and the predictive block. An intra-coded blockis encoded according to an intra-coding mode and the residual data. Forfurther compression, the residual data may be transformed from the pixeldomain to a transform domain. These result in residual transformcoefficients, which may be quantized. The quantized transformcoefficients may initially be arranged in a two-dimensional array. Thequantized transform coefficients may be scanned in order to produce aone-dimensional vector of transform coefficients. Entropy coding may beapplied to achieve even more compression. Such video compressiontechniques are discussed in greater detail below.

To ensure an encoded video can be accurately decoded, video is encodedand decoded according to corresponding video coding standards. Videocoding standards include International Telecommunication Union (ITU)Standardization Sector (ITU-T) H.261, International Organization forStandardization/International Electrotechnical Commission (ISO/IEC)Motion Picture Experts Group (MPEG)-1 Part 2, ITU-T H.262 or ISO/IECMPEG-2 Part 2, ITU-T H.263, ISO/IEC MPEG-4 Part 2, Advanced Video Coding(AVC), also known as ITU-T H.264 or ISO/IEC MPEG-4 Part 10, and HighEfficiency Video Coding (HEVC), also known as ITU-T H.265 or MPEG-H Part2. AVC includes extensions such as Scalable Video Coding (SVC),Multiview Video Coding (MVC) and Multiview Video Coding plus Depth(MVC+D), and three dimensional (3D) AVC (3D-AVC). HEVC includesextensions such as Scalable HEVC (SHVC), Multiview HEVC (MV-HEVC), and3D HEVC (3D-HEVC). The joint video experts team (JVET) of ITU-T andISO/IEC has begun developing a video coding standard referred to asVersatile Video Coding (VVC). VVC is included in a Working Draft (WD),which includes JVET-02001-v14.

Video coding systems may encode a video sequence into a bitstream as aseries of coded pictures. Various parameters can also be coded tosupport decoding of the video sequence. For example, a video parameterset (VP S) may contain parameters related to the configuration oflayers, sublayers, and/or output layer sets (OLSs) in the videosequence. In addition, the video sequence can be checked by ahypothetical reference decoder (HRD) for conformance with standards. Tosupport such conformance testing, the VPS and/or the SPS may contain HRDparameters. HRD related parameters may also be contained in supplementalenhancement information (SEI) messages. A SEI message containsinformation that is not needed by the decoding process in order todetermine the values of the samples in decoded pictures. For example,the SEI messages may contain HRD parameters that further describe theHRD process in light of the HRD parameters contained in the VPS. In somevideo coding systems, the SEI messages may contain parameters thatdirectly reference the VPS. This dependency creates certaindifficulties. For example, the VPS may be removed from a bitstream whentransmitting an OLS that contains a single layer. This approach may bebeneficial in some instances as the VPS does not contain usefulinformation when the decoder only receives one layer. However, omittingthe VPS can prevent the SEI messages from being properly parsed due tothe dependency on the VPS. Specifically, omitting the VPS can cause theSEI messages to return an error as the data upon which they depend inthe VPS is not received at the decoder.

Disclosed herein is a mechanism to remove dependencies between the VPSand the SEI messages. For example, a decoding unit (DU) hypotheticalreference decoder (HRD) parameters present flag(du_hrd_params_present_flag) can be coded in a current SEI message. Thedu_hrd_params_present_flag specifies whether the HRD should operate onan access unit (AU) level or a decoding unit (DU) level. Further, thecurrent SEI message can include a DU coded picture buffer (CPB)parameters in picture timing (PT) SEI flag(du_cpb_params_in_pic_timing_sei_flag) that specifies whether DU levelCPB removal delay parameters are present in a PT SEI message or adecoding unit information (DUI) SEI message. By including these flags inthe current SEI message, the current SEI message does not depend on theVPS. Hence, the current SEI message can be parsed even when the VPS isomitted from the bitstream. Accordingly, various errors may be avoided.As a result, the functionality of the encoder and the decoder isincreased. Further, removing the dependency between the SEI messages andthe VPS supports removal of the VPS in certain cases, which increasescoding efficiency, and hence reduces processor, memory, and/or networksignaling resource usage at both the encoder and the decoder.

FIG. 1 is a flowchart of an example operating method 100 of coding avideo signal. Specifically, a video signal is encoded at an encoder. Theencoding process compresses the video signal by employing variousmechanisms to reduce the video file size. A smaller file size allows thecompressed video file to be transmitted toward a user, while reducingassociated bandwidth overhead. The decoder then decodes the compressedvideo file to reconstruct the original video signal for display to anend user. The decoding process generally mirrors the encoding process toallow the decoder to consistently reconstruct the video signal.

At step 101, the video signal is input into the encoder. For example,the video signal may be an uncompressed video file stored in memory. Asanother example, the video file may be captured by a video capturedevice, such as a video camera, and encoded to support live streaming ofthe video. The video file may include both an audio component and avideo component. The video component contains a series of image framesthat, when viewed in a sequence, gives the visual impression of motion.The frames contain pixels that are expressed in terms of light, referredto herein as luma components (or luma samples), and color, which isreferred to as chroma components (or color samples). In some examples,the frames may also contain depth values to support three dimensionalviewing.

At step 103, the video is partitioned into blocks. Partitioning includessubdividing the pixels in each frame into square and/or rectangularblocks for compression. For example, in High Efficiency Video Coding(HEVC) (also known as H.265 and MPEG-H Part 2) the frame can first bedivided into coding tree units (CTUs), which are blocks of a predefinedsize (e.g., sixty-four pixels by sixty-four pixels). The CTUs containboth luma and chroma samples. Coding trees may be employed to divide theCTUs into blocks and then recursively subdivide the blocks untilconfigurations are achieved that support further encoding. For example,luma components of a frame may be subdivided until the individual blockscontain relatively homogenous lighting values. Further, chromacomponents of a frame may be subdivided until the individual blockscontain relatively homogenous color values. Accordingly, partitioningmechanisms vary depending on the content of the video frames.

At step 105, various compression mechanisms are employed to compress theimage blocks partitioned at step 103. For example, inter-predictionand/or intra-prediction may be employed. Inter-prediction is designed totake advantage of the fact that objects in a common scene tend to appearin successive frames. Accordingly, a block depicting an object in areference frame need not be repeatedly described in adjacent frames.Specifically, an object, such as a table, may remain in a constantposition over multiple frames. Hence the table is described once andadjacent frames can refer back to the reference frame. Pattern matchingmechanisms may be employed to match objects over multiple frames.Further, moving objects may be represented across multiple frames, forexample due to object movement or camera movement. As a particularexample, a video may show an automobile that moves across the screenover multiple frames. Motion vectors can be employed to describe suchmovement. A motion vector is a two-dimensional vector that provides anoffset from the coordinates of an object in a frame to the coordinatesof the object in a reference frame. As such, inter-prediction can encodean image block in a current frame as a set of motion vectors indicatingan offset from a corresponding block in a reference frame.

Intra-prediction encodes blocks in a common frame. Intra-predictiontakes advantage of the fact that luma and chroma components tend tocluster in a frame. For example, a patch of green in a portion of a treetends to be positioned adjacent to similar patches of green.Intra-prediction employs multiple directional prediction modes (e.g.,thirty-three in HEVC), a planar mode, and a direct current (DC) mode.The directional modes indicate that a current block is similar/the sameas samples of a neighbor block in a corresponding direction. Planar modeindicates that a series of blocks along a row/column (e.g., a plane) canbe interpolated based on neighbor blocks at the edges of the row. Planarmode, in effect, indicates a smooth transition of light/color across arow/column by employing a relatively constant slope in changing values.DC mode is employed for boundary smoothing and indicates that a block issimilar/the same as an average value associated with samples of all theneighbor blocks associated with the angular directions of thedirectional prediction modes. Accordingly, intra-prediction blocks canrepresent image blocks as various relational prediction mode valuesinstead of the actual values. Further, inter-prediction blocks canrepresent image blocks as motion vector values instead of the actualvalues. In either case, the prediction blocks may not exactly representthe image blocks in some cases. Any differences are stored in residualblocks. Transforms may be applied to the residual blocks to furthercompress the file.

At step 107, various filtering techniques may be applied. In HEVC, thefilters are applied according to an in-loop filtering scheme. The blockbased prediction discussed above may result in the creation of blockyimages at the decoder. Further, the block based prediction scheme mayencode a block and then reconstruct the encoded block for later use as areference block. The in-loop filtering scheme iteratively applies noisesuppression filters, de-blocking filters, adaptive loop filters, andsample adaptive offset (SAO) filters to the blocks/frames. These filtersmitigate such blocking artifacts so that the encoded file can beaccurately reconstructed. Further, these filters mitigate artifacts inthe reconstructed reference blocks so that artifacts are less likely tocreate additional artifacts in subsequent blocks that are encoded basedon the reconstructed reference blocks.

Once the video signal has been partitioned, compressed, and filtered,the resulting data is encoded in a bitstream at step 109. The bitstreamincludes the data discussed above as well as any signaling data desiredto support proper video signal reconstruction at the decoder. Forexample, such data may include partition data, prediction data, residualblocks, and various flags providing coding instructions to the decoder.The bitstream may be stored in memory for transmission toward a decoderupon request. The bitstream may also be broadcast and/or multicasttoward a plurality of decoders. The creation of the bitstream is aniterative process. Accordingly, steps 101, 103, 105, 107, and 109 mayoccur continuously and/or simultaneously over many frames and blocks.The order shown in FIG. 1 is presented for clarity and ease ofdiscussion, and is not intended to limit the video coding process to aparticular order.

The decoder receives the bitstream and begins the decoding process atstep 111. Specifically, the decoder employs an entropy decoding schemeto convert the bitstream into corresponding syntax and video data. Thedecoder employs the syntax data from the bitstream to determine thepartitions for the frames at step 111. The partitioning should match theresults of block partitioning at step 103. Entropy encoding/decoding asemployed in step 111 is now described. The encoder makes many choicesduring the compression process, such as selecting block partitioningschemes from several possible choices based on the spatial positioningof values in the input image(s). Signaling the exact choices may employa large number of bins. As used herein, a bin is a binary value that istreated as a variable (e.g., a bit value that may vary depending oncontext). Entropy coding allows the encoder to discard any options thatare clearly not viable for a particular case, leaving a set of allowableoptions. Each allowable option is then assigned a code word. The lengthof the code words is based on the number of allowable options (e.g., onebin for two options, two bins for three to four options, etc.) Theencoder then encodes the code word for the selected option. This schemereduces the size of the code words as the code words are as big asdesired to uniquely indicate a selection from a small sub-set ofallowable options as opposed to uniquely indicating the selection from apotentially large set of all possible options. The decoder then decodesthe selection by determining the set of allowable options in a similarmanner to the encoder. By determining the set of allowable options, thedecoder can read the code word and determine the selection made by theencoder.

At step 113, the decoder performs block decoding. Specifically, thedecoder employs reverse transforms to generate residual blocks. Then thedecoder employs the residual blocks and corresponding prediction blocksto reconstruct the image blocks according to the partitioning. Theprediction blocks may include both intra-prediction blocks andinter-prediction blocks as generated at the encoder at step 105. Thereconstructed image blocks are then positioned into frames of areconstructed video signal according to the partitioning data determinedat step 111. Syntax for step 113 may also be signaled in the bitstreamvia entropy coding as discussed above.

At step 115, filtering is performed on the frames of the reconstructedvideo signal in a manner similar to step 107 at the encoder. Forexample, noise suppression filters, de-blocking filters, adaptive loopfilters, and SAO filters may be applied to the frames to remove blockingartifacts. Once the frames are filtered, the video signal can be outputto a display at step 117 for viewing by an end user.

FIG. 2 is a schematic diagram of an example coding and decoding (codec)system 200 for video coding. Specifically, codec system 200 providesfunctionality to support the implementation of operating method 100.Codec system 200 is generalized to depict components employed in both anencoder and a decoder. Codec system 200 receives and partitions a videosignal as discussed with respect to steps 101 and 103 in operatingmethod 100, which results in a partitioned video signal 201. Codecsystem 200 then compresses the partitioned video signal 201 into a codedbitstream when acting as an encoder as discussed with respect to steps105, 107, and 109 in method 100. When acting as a decoder, codec system200 generates an output video signal from the bitstream as discussedwith respect to steps 111, 113, 115, and 117 in operating method 100.The codec system 200 includes a general coder control component 211, atransform scaling and quantization component 213, an intra-pictureestimation component 215, an intra-picture prediction component 217, amotion compensation component 219, a motion estimation component 221, ascaling and inverse transform component 229, a filter control analysiscomponent 227, an in-loop filters component 225, a decoded picturebuffer component 223, and a header formatting and context adaptivebinary arithmetic coding (CABAC) component 231. Such components arecoupled as shown. In FIG. 2, black lines indicate movement of data to beencoded/decoded while dashed lines indicate movement of control datathat controls the operation of other components. The components of codecsystem 200 may all be present in the encoder. The decoder may include asubset of the components of codec system 200. For example, the decodermay include the intra-picture prediction component 217, the motioncompensation component 219, the scaling and inverse transform component229, the in-loop filters component 225, and the decoded picture buffercomponent 223. These components are now described.

The partitioned video signal 201 is a captured video sequence that hasbeen partitioned into blocks of pixels by a coding tree. A coding treeemploys various split modes to subdivide a block of pixels into smallerblocks of pixels. These blocks can then be further subdivided intosmaller blocks. The blocks may be referred to as nodes on the codingtree. Larger parent nodes are split into smaller child nodes. The numberof times a node is subdivided is referred to as the depth of thenode/coding tree. The divided blocks can be included in coding units(CUs) in some cases. For example, a CU can be a sub-portion of a CTUthat contains a luma block, red difference chroma (Cr) block(s), and ablue difference chroma (Cb) block(s) along with corresponding syntaxinstructions for the CU. The split modes may include a binary tree (BT),triple tree (TT), and a quad tree (QT) employed to partition a node intotwo, three, or four child nodes, respectively, of varying shapesdepending on the split modes employed. The partitioned video signal 201is forwarded to the general coder control component 211, the transformscaling and quantization component 213, the intra-picture estimationcomponent 215, the filter control analysis component 227, and the motionestimation component 221 for compression.

The general coder control component 211 is configured to make decisionsrelated to coding of the images of the video sequence into the bitstreamaccording to application constraints. For example, the general codercontrol component 211 manages optimization of bitrate/bitstream sizeversus reconstruction quality. Such decisions may be made based onstorage space/bandwidth availability and image resolution requests. Thegeneral coder control component 211 also manages buffer utilization inlight of transmission speed to mitigate buffer underrun and overrunissues. To manage these issues, the general coder control component 211manages partitioning, prediction, and filtering by the other components.For example, the general coder control component 211 may dynamicallyincrease compression complexity to increase resolution and increasebandwidth usage or decrease compression complexity to decreaseresolution and bandwidth usage. Hence, the general coder controlcomponent 211 controls the other components of codec system 200 tobalance video signal reconstruction quality with bit rate concerns. Thegeneral coder control component 211 creates control data, which controlsthe operation of the other components. The control data is alsoforwarded to the header formatting and CABAC component 231 to be encodedin the bitstream to signal parameters for decoding at the decoder.

The partitioned video signal 201 is also sent to the motion estimationcomponent 221 and the motion compensation component 219 forinter-prediction. A frame or slice of the partitioned video signal 201may be divided into multiple video blocks. Motion estimation component221 and the motion compensation component 219 perform inter-predictivecoding of the received video block relative to one or more blocks in oneor more reference frames to provide temporal prediction. Codec system200 may perform multiple coding passes, e.g., to select an appropriatecoding mode for each block of video data.

Motion estimation component 221 and motion compensation component 219may be highly integrated, but are illustrated separately for conceptualpurposes. Motion estimation, performed by motion estimation component221, is the process of generating motion vectors, which estimate motionfor video blocks. A motion vector, for example, may indicate thedisplacement of a coded object relative to a predictive block. Apredictive block is a block that is found to closely match the block tobe coded, in terms of pixel difference. A predictive block may also bereferred to as a reference block. Such pixel difference may bedetermined by sum of absolute difference (SAD), sum of square difference(SSD), or other difference metrics. HEVC employs several coded objectsincluding a CTU, coding tree blocks (CTBs), and CUs. For example, a CTUcan be divided into CTBs, which can then be divided into CBs forinclusion in CUs. A CU can be encoded as a prediction unit containingprediction data and/or a transform unit (TU) containing transformedresidual data for the CU. The motion estimation component 221 generatesmotion vectors, prediction units, and TUs by using a rate-distortionanalysis as part of a rate distortion optimization process. For example,the motion estimation component 221 may determine multiple referenceblocks, multiple motion vectors, etc. for a current block/frame, and mayselect the reference blocks, motion vectors, etc. having the bestrate-distortion characteristics. The best rate-distortioncharacteristics balance both quality of video reconstruction (e.g.,amount of data loss by compression) with coding efficiency (e.g., sizeof the final encoding).

In some examples, codec system 200 may calculate values for sub-integerpixel positions of reference pictures stored in decoded picture buffercomponent 223. For example, video codec system 200 may interpolatevalues of one-quarter pixel positions, one-eighth pixel positions, orother fractional pixel positions of the reference picture. Therefore,motion estimation component 221 may perform a motion search relative tothe full pixel positions and fractional pixel positions and output amotion vector with fractional pixel precision. The motion estimationcomponent 221 calculates a motion vector for a prediction unit of avideo block in an inter-coded slice by comparing the position of theprediction unit to the position of a predictive block of a referencepicture. Motion estimation component 221 outputs the calculated motionvector as motion data to header formatting and CABAC component 231 forencoding and motion to the motion compensation component 219.

Motion compensation, performed by motion compensation component 219, mayinvolve fetching or generating the predictive block based on the motionvector determined by motion estimation component 221. Again, motionestimation component 221 and motion compensation component 219 may befunctionally integrated, in some examples. Upon receiving the motionvector for the prediction unit of the current video block, motioncompensation component 219 may locate the predictive block to which themotion vector points. A residual video block is then formed bysubtracting pixel values of the predictive block from the pixel valuesof the current video block being coded, forming pixel difference values.In general, motion estimation component 221 performs motion estimationrelative to luma components, and motion compensation component 219 usesmotion vectors calculated based on the luma components for both chromacomponents and luma components. The predictive block and residual blockare forwarded to transform scaling and quantization component 213.

The partitioned video signal 201 is also sent to intra-pictureestimation component 215 and intra-picture prediction component 217. Aswith motion estimation component 221 and motion compensation component219, intra-picture estimation component 215 and intra-picture predictioncomponent 217 may be highly integrated, but are illustrated separatelyfor conceptual purposes. The intra-picture estimation component 215 andintra-picture prediction component 217 intra-predict a current blockrelative to blocks in a current frame, as an alternative to theinter-prediction performed by motion estimation component 221 and motioncompensation component 219 between frames, as described above. Inparticular, the intra-picture estimation component 215 determines anintra-prediction mode to use to encode a current block. In someexamples, intra-picture estimation component 215 selects an appropriateintra-prediction mode to encode a current block from multiple testedintra-prediction modes. The selected intra-prediction modes are thenforwarded to the header formatting and CABAC component 231 for encoding.

For example, the intra-picture estimation component 215 calculatesrate-distortion values using a rate-distortion analysis for the varioustested intra-prediction modes, and selects the intra-prediction modehaving the best rate-distortion characteristics among the tested modes.Rate-distortion analysis generally determines an amount of distortion(or error) between an encoded block and an original unencoded block thatwas encoded to produce the encoded block, as well as a bitrate (e.g., anumber of bits) used to produce the encoded block. The intra-pictureestimation component 215 calculates ratios from the distortions andrates for the various encoded blocks to determine which intra-predictionmode exhibits the best rate-distortion value for the block. In addition,intra-picture estimation component 215 may be configured to code depthblocks of a depth map using a depth modeling mode (DMM) based onrate-distortion optimization (RDO).

The intra-picture prediction component 217 may generate a residual blockfrom the predictive block based on the selected intra-prediction modesdetermined by intra-picture estimation component 215 when implemented onan encoder or read the residual block from the bitstream whenimplemented on a decoder. The residual block includes the difference invalues between the predictive block and the original block, representedas a matrix. The residual block is then forwarded to the transformscaling and quantization component 213. The intra-picture estimationcomponent 215 and the intra-picture prediction component 217 may operateon both luma and chroma components.

The transform scaling and quantization component 213 is configured tofurther compress the residual block. The transform scaling andquantization component 213 applies a transform, such as a discretecosine transform (DCT), a discrete sine transform (DST), or aconceptually similar transform, to the residual block, producing a videoblock comprising residual transform coefficient values. Wavelettransforms, integer transforms, sub-band transforms or other types oftransforms could also be used. The transform may convert the residualinformation from a pixel value domain to a transform domain, such as afrequency domain. The transform scaling and quantization component 213is also configured to scale the transformed residual information, forexample based on frequency. Such scaling involves applying a scalefactor to the residual information so that different frequencyinformation is quantized at different granularities, which may affectfinal visual quality of the reconstructed video. The transform scalingand quantization component 213 is also configured to quantize thetransform coefficients to further reduce bit rate. The quantizationprocess may reduce the bit depth associated with some or all of thecoefficients. The degree of quantization may be modified by adjusting aquantization parameter. In some examples, the transform scaling andquantization component 213 may then perform a scan of the matrixincluding the quantized transform coefficients. The quantized transformcoefficients are forwarded to the header formatting and CABAC component231 to be encoded in the bitstream.

The scaling and inverse transform component 229 applies a reverseoperation of the transform scaling and quantization component 213 tosupport motion estimation. The scaling and inverse transform component229 applies inverse scaling, transformation, and/or quantization toreconstruct the residual block in the pixel domain, e.g., for later useas a reference block which may become a predictive block for anothercurrent block. The motion estimation component 221 and/or motioncompensation component 219 may calculate a reference block by adding theresidual block back to a corresponding predictive block for use inmotion estimation of a later block/frame. Filters are applied to thereconstructed reference blocks to mitigate artifacts created duringscaling, quantization, and transform. Such artifacts could otherwisecause inaccurate prediction (and create additional artifacts) whensubsequent blocks are predicted.

The filter control analysis component 227 and the in-loop filterscomponent 225 apply the filters to the residual blocks and/or toreconstructed image blocks. For example, the transformed residual blockfrom the scaling and inverse transform component 229 may be combinedwith a corresponding prediction block from intra-picture predictioncomponent 217 and/or motion compensation component 219 to reconstructthe original image block. The filters may then be applied to thereconstructed image block. In some examples, the filters may instead beapplied to the residual blocks. As with other components in FIG. 2, thefilter control analysis component 227 and the in-loop filters component225 are highly integrated and may be implemented together, but aredepicted separately for conceptual purposes. Filters applied to thereconstructed reference blocks are applied to particular spatial regionsand include multiple parameters to adjust how such filters are applied.The filter control analysis component 227 analyzes the reconstructedreference blocks to determine where such filters should be applied andsets corresponding parameters. Such data is forwarded to the headerformatting and CABAC component 231 as filter control data for encoding.The in-loop filters component 225 applies such filters based on thefilter control data. The filters may include a deblocking filter, anoise suppression filter, a SAO filter, and an adaptive loop filter.Such filters may be applied in the spatial/pixel domain (e.g., on areconstructed pixel block) or in the frequency domain, depending on theexample.

When operating as an encoder, the filtered reconstructed image block,residual block, and/or prediction block are stored in the decodedpicture buffer component 223 for later use in motion estimation asdiscussed above. When operating as a decoder, the decoded picture buffercomponent 223 stores and forwards the reconstructed and filtered blockstoward a display as part of an output video signal. The decoded picturebuffer component 223 may be any memory device capable of storingprediction blocks, residual blocks, and/or reconstructed image blocks.

The header formatting and CABAC component 231 receives the data from thevarious components of codec system 200 and encodes such data into acoded bitstream for transmission toward a decoder. Specifically, theheader formatting and CABAC component 231 generates various headers toencode control data, such as general control data and filter controldata. Further, prediction data, including intra-prediction and motiondata, as well as residual data in the form of quantized transformcoefficient data are all encoded in the bitstream. The final bitstreamincludes all information desired by the decoder to reconstruct theoriginal partitioned video signal 201. Such information may also includeintra-prediction mode index tables (also referred to as codeword mappingtables), definitions of encoding contexts for various blocks,indications of most probable intra-prediction modes, an indication ofpartition information, etc. Such data may be encoded by employingentropy coding. For example, the information may be encoded by employingcontext adaptive variable length coding (CAVLC), CABAC, syntax-basedcontext-adaptive binary arithmetic coding (SBAC), probability intervalpartitioning entropy (PIPE) coding, or another entropy coding technique.Following the entropy coding, the coded bitstream may be transmitted toanother device (e.g., a video decoder) or archived for latertransmission or retrieval.

FIG. 3 is a block diagram illustrating an example video encoder 300.Video encoder 300 may be employed to implement the encoding functions ofcodec system 200 and/or implement steps 101, 103, 105, 107, and/or 109of operating method 100. Encoder 300 partitions an input video signal,resulting in a partitioned video signal 301, which is substantiallysimilar to the partitioned video signal 201. The partitioned videosignal 301 is then compressed and encoded into a bitstream by componentsof encoder 300.

Specifically, the partitioned video signal 301 is forwarded to anintra-picture prediction component 317 for intra-prediction. Theintra-picture prediction component 317 may be substantially similar tointra-picture estimation component 215 and intra-picture predictioncomponent 217. The partitioned video signal 301 is also forwarded to amotion compensation component 321 for inter-prediction based onreference blocks in a decoded picture buffer component 323. The motioncompensation component 321 may be substantially similar to motionestimation component 221 and motion compensation component 219. Theprediction blocks and residual blocks from the intra-picture predictioncomponent 317 and the motion compensation component 321 are forwarded toa transform and quantization component 313 for transform andquantization of the residual blocks. The transform and quantizationcomponent 313 may be substantially similar to the transform scaling andquantization component 213. The transformed and quantized residualblocks and the corresponding prediction blocks (along with associatedcontrol data) are forwarded to an entropy coding component 331 forcoding into a bitstream. The entropy coding component 331 may besubstantially similar to the header formatting and CABAC component 231.

The transformed and quantized residual blocks and/or the correspondingprediction blocks are also forwarded from the transform and quantizationcomponent 313 to an inverse transform and quantization component 329 forreconstruction into reference blocks for use by the motion compensationcomponent 321. The inverse transform and quantization component 329 maybe substantially similar to the scaling and inverse transform component229. In-loop filters in an in-loop filters component 325 are alsoapplied to the residual blocks and/or reconstructed reference blocks,depending on the example. The in-loop filters component 325 may besubstantially similar to the filter control analysis component 227 andthe in-loop filters component 225. The in-loop filters component 325 mayinclude multiple filters as discussed with respect to in-loop filterscomponent 225. The filtered blocks are then stored in a decoded picturebuffer component 323 for use as reference blocks by the motioncompensation component 321. The decoded picture buffer component 323 maybe substantially similar to the decoded picture buffer component 223.

FIG. 4 is a block diagram illustrating an example video decoder 400.Video decoder 400 may be employed to implement the decoding functions ofcodec system 200 and/or implement steps 111, 113, 115, and/or 117 ofoperating method 100. Decoder 400 receives a bitstream, for example froman encoder 300, and generates a reconstructed output video signal basedon the bitstream for display to an end user.

The bitstream is received by an entropy decoding component 433. Theentropy decoding component 433 is configured to implement an entropydecoding scheme, such as CAVLC, CABAC, SBAC, PIPE coding, or otherentropy coding techniques. For example, the entropy decoding component433 may employ header information to provide a context to interpretadditional data encoded as codewords in the bitstream. The decodedinformation includes any desired information to decode the video signal,such as general control data, filter control data, partitioninformation, motion data, prediction data, and quantized transformcoefficients from residual blocks. The quantized transform coefficientsare forwarded to an inverse transform and quantization component 429 forreconstruction into residual blocks. The inverse transform andquantization component 429 may be similar to inverse transform andquantization component 329.

The reconstructed residual blocks and/or prediction blocks are forwardedto intra-picture prediction component 417 for reconstruction into imageblocks based on intra-prediction operations. The intra-pictureprediction component 417 may be similar to intra-picture estimationcomponent 215 and an intra-picture prediction component 217.Specifically, the intra-picture prediction component 417 employsprediction modes to locate a reference block in the frame and applies aresidual block to the result to reconstruct intra-predicted imageblocks. The reconstructed intra-predicted image blocks and/or theresidual blocks and corresponding inter-prediction data are forwarded toa decoded picture buffer component 423 via an in-loop filters component425, which may be substantially similar to decoded picture buffercomponent 223 and in-loop filters component 225, respectively. Thein-loop filters component 425 filters the reconstructed image blocks,residual blocks and/or prediction blocks, and such information is storedin the decoded picture buffer component 423. Reconstructed image blocksfrom decoded picture buffer component 423 are forwarded to a motioncompensation component 421 for inter-prediction. The motion compensationcomponent 421 may be substantially similar to motion estimationcomponent 221 and/or motion compensation component 219. Specifically,the motion compensation component 421 employs motion vectors from areference block to generate a prediction block and applies a residualblock to the result to reconstruct an image block. The resultingreconstructed blocks may also be forwarded via the in-loop filterscomponent 425 to the decoded picture buffer component 423. The decodedpicture buffer component 423 continues to store additional reconstructedimage blocks, which can be reconstructed into frames via the partitioninformation. Such frames may also be placed in a sequence. The sequenceis output toward a display as a reconstructed output video signal.

FIG. 5 is a schematic diagram illustrating an example HRD 500. A HRD 500may be employed in an encoder, such as codec system 200 and/or encoder300. The HRD 500 may check the bitstream created at step 109 of method100 before the bitstream is forwarded to a decoder, such as decoder 400.In some examples, the bitstream may be continuously forwarded throughthe HRD 500 as the bitstream is encoded. In the event that a portion ofthe bitstream fails to conform to associated constraints, the HRD 500can indicate such failure to an encoder to cause the encoder tore-encode the corresponding section of the bitstream with differentmechanisms.

The HRD 500 includes a hypothetical stream scheduler (HSS) 541. A HSS541 is a component configured to perform a hypothetical deliverymechanism. The hypothetical delivery mechanism is used for checking theconformance of a bitstream or a decoder with regards to the timing anddata flow of a bitstream 551 input into the HRD 500. For example, theHSS 541 may receive a bitstream 551 output from an encoder and managethe conformance testing process on the bitstream 551. In a particularexample, the HSS 541 can control the rate that coded pictures movethrough the HRD 500 and verify that the bitstream 551 does not containnon-conforming data.

The HSS 541 may forward the bitstream 551 to a CPB 543 at a predefinedrate. The HRD 500 may manage data in decoding units (DU) 553. A DU 553is an Access Unit (AU) or a sub-set of an AU and associated non-videocoding layer (VCL) network abstraction layer (NAL) units. Specifically,an AU contains one or more pictures associated with an output time. Forexample, an AU may contain a single picture in a single layer bitstream,and may contain a picture for each layer in a multi-layer bitstream.Each picture of an AU may be divided into slices that are each includedin a corresponding VCL NAL unit. Hence, a DU 553 may contain one or morepictures, one or more slices of a picture, or combinations thereof.Also, parameters used to decode the AU, pictures, and/or slices can beincluded in non-VCL NAL units. As such, the DU 553 contains non-VCL NALunits that contain data needed to support decoding the VCL NAL units inthe DU 553. The CPB 543 is a first-in first-out buffer in the HRD 500.The CPB 543 contains DUs 553 including video data in decoding order. TheCPB 543 stores the video data for use during bitstream conformanceverification.

The CPB 543 forwards the DUs 553 to a decoding process component 545.The decoding process component 545 is a component that conforms to theVVC standard. For example, the decoding process component 545 mayemulate a decoder 400 employed by an end user. The decoding processcomponent 545 decodes the DUs 553 at a rate that can be achieved by anexample end user decoder. If the decoding process component 545 cannotdecode the DUs 553 fast enough to prevent an overflow of the CPB 543,then the bitstream 551 does not conform to the standard and should bere-encoded.

The decoding process component 545 decodes the DUs 553, which createsdecoded DUs 555. A decoded DU 555 contains a decoded picture. Thedecoded DUs 555 are forwarded to a DPB 547. The DPB 547 may besubstantially similar to a decoded picture buffer component 223, 323,and/or 423. To support inter-prediction, pictures that are marked foruse as reference pictures 556 that are obtained from the decoded DUs 555are returned to the decoding process component 545 to support furtherdecoding. The DPB 547 outputs the decoded video sequence as a series ofpictures 557. The pictures 557 are reconstructed pictures that generallymirror pictures encoded into the bitstream 551 by the encoder.

The pictures 557 are forwarded to an output cropping component 549. Theoutput cropping component 549 is configured to apply a conformancecropping window to the pictures 557. This results in output croppedpictures 559. An output cropped picture 559 is a completelyreconstructed picture. Accordingly, the output cropped picture 559mimics what an end user would see upon decoding the bitstream 551. Assuch, the encoder can review the output cropped pictures 559 to ensurethe encoding is satisfactory.

The HRD 500 is initialized based on HRD parameters in the bitstream 551.For example, the HRD 500 may read HRD parameters from a VPS, a SPS,and/or SEI messages. The HRD 500 may then perform conformance testingoperations on the bitstream 551 based on the information in such HRDparameters. As a specific example, the HRD 500 may determine one or moreCPB delivery schedules from the HRD parameters. A delivery schedulespecifies timing for delivery of video data to and/or from a memorylocation, such as a CPB and/or a DPB. Hence, a CPB delivery schedulespecifies timing for delivery of AUs, DUs 553, and/or pictures, to/fromthe CPB 543. It should be noted that the HRD 500 may employ DPB deliveryschedules for the DPB 547 that are similar to the CPB deliveryschedules.

Video may be coded into different layers and/or OLSs for use by decoderswith varying levels of hardware capabilities as well for varying networkconditions. The CPB delivery schedules are selected to reflect theseissues. Accordingly, higher layer sub-bitstreams are designated foroptimal hardware and network conditions and hence higher layers mayreceive one or more CPB delivery schedules that employ a large amount ofmemory in the CPB 543 and short delays for transfers of the DUs 553toward the DPB 547. Likewise, lower layer sub-bitstreams are designatedfor limited decoder hardware capabilities and/or poor networkconditions. Hence, lower layers may receive one or more CPB deliveryschedules that employ a small amount of memory in the CPB 543 and longerdelays for transfers of the DUs 553 toward the DPB 547. The OLSs,layers, sublayers, or combinations thereof can then be tested accordingto the corresponding delivery schedule to ensure that the resultingsub-bitstream can be correctly decoded under the conditions that areexpected for the sub-bitstream. Accordingly, the HRD parameters in thebitstream 551 can indicate the CPB delivery schedules as well as includesufficient data to allow the HRD 500 to determine the CPB deliveryschedules and correlate the CPB delivery schedules to the correspondingOLSs, layers, and/or sublayers.

FIG. 6 is a schematic diagram illustrating an example multi-layer videosequence 600. The multi-layer video sequence 600 may be encoded by anencoder, such as codec system 200 and/or encoder 300 and decoded by adecoder, such as codec system 200 and/or decoder 400, for exampleaccording to method 100. Further, the multi-layer video sequence 600 canbe checked for standard conformance by a HRD, such as HRD 500. Themulti-layer video sequence 600 is included to depict an exampleapplication for layers in a coded video sequence. A multi-layer videosequence 600 is any video sequence that employs a plurality of layers,such as layer N 631 and layer N+1 632.

In an example, the multi-layer video sequence 600 may employ inter-layerprediction 621. Inter-layer prediction 621 is applied between pictures611, 612, 613, and 614 and pictures 615, 616, 617, and 618 in differentlayers. In the example shown, pictures 611, 612, 613, and 614 are partof layer N+1 632 and pictures 615, 616, 617, and 618 are part of layer N631. A layer, such as layer N 631 and/or layer N+1 632, is a group ofpictures that are all associated with a similar value of acharacteristic, such as a similar size, quality, resolution, signal tonoise ratio, capability, etc. A layer may be defined formally as a setof VCL NAL units that share the same layer ID and associated non-VCL NALunits. A VCL NAL unit is a NAL unit coded to contain video data, such asa coded slice of a picture. A non-VCL NAL unit is a NAL unit thatcontains non-video data such as syntax and/or parameters that supportdecoding the video data, performance of conformance checking, or otheroperations.

In the example shown, layer N+1 632 is associated with a larger imagesize than layer N 631. Accordingly, pictures 611, 612, 613, and 614 inlayer N+1 632 have a larger picture size (e.g., larger height and widthand hence more samples) than pictures 615, 616, 617, and 618 in layer N631 in this example. However, such pictures can be separated betweenlayer N+1 632 and layer N 631 by other characteristics. While only twolayers, layer N+1 632 and layer N 631, are shown, a set of pictures canbe separated into any number of layers based on associatedcharacteristics. Layer N+1 632 and layer N 631 may also be denoted by alayer ID. A layer ID is an item of data that is associated with apicture and denotes the picture is part of an indicated layer.Accordingly, each picture 611-618 may be associated with a correspondinglayer ID to indicate which layer N+1 632 or layer N 631 includes thecorresponding picture. For example, a layer ID may include a NAL unitheader layer ID (nuh_layer_id), which is a syntax element that specifiesan identifier of a layer that includes a NAL unit (e.g., that includeslices and/or parameters of the pictures in a layer). A layer associatedwith a lower quality/smaller image size/smaller bitstream size, such aslayer N 631, is generally assigned a lower layer ID and is referred toas a lower layer. Further, a layer associated with a higherquality/larger image size/larger bitstream size, such as layer N+1 632,is generally assigned a higher layer ID and is referred to as a higherlayer.

Pictures 611-618 in different layers 631-632 are configured to bedisplayed in the alternative. As a specific example, a decoder maydecode and display picture 615 at a current display time if a smallerpicture is desired or the decoder may decode and display picture 611 atthe current display time if a larger picture is desired. As such,pictures 611-614 at higher layer N+1 632 contain substantially the sameimage data as corresponding pictures 615-618 at lower layer N 631(notwithstanding the difference in picture size). Specifically, picture611 contains substantially the same image data as picture 615, picture612 contains substantially the same image data as picture 616, etc.

Pictures 611-618 can be coded by reference to other pictures 611-618 inthe same layer N 631 or N+1 632. Coding a picture in reference toanother picture in the same layer results in inter-prediction 623.Inter-prediction 623 is depicted by solid line arrows. For example,picture 613 may be coded by employing inter-prediction 623 using one ortwo of pictures 611, 612, and/or 614 in layer N+1 632 as a reference,where one picture is referenced for unidirectional inter-predictionand/or two pictures are referenced for bidirectional inter-prediction.Further, picture 617 may be coded by employing inter-prediction 623using one or two of pictures 615, 616, and/or 618 in layer N 631 as areference, where one picture is referenced for unidirectionalinter-prediction and/or two pictures are referenced for bidirectionalinter-prediction. When a picture is used as a reference for anotherpicture in the same layer when performing inter-prediction 623, thepicture may be referred to as a reference picture. For example, picture612 may be a reference picture used to code picture 613 according tointer-prediction 623. Inter-prediction 623 can also be referred to asintra-layer prediction in a multi-layer context. As such,inter-prediction 623 is a mechanism of coding samples of a currentpicture by reference to indicated samples in a reference picture that isdifferent from the current picture where the reference picture and thecurrent picture are in the same layer.

Pictures 611-618 can also be coded by reference to other pictures611-618 in different layers. This process is known as inter-layerprediction 621, and is depicted by dashed arrows. Inter-layer prediction621 is a mechanism of coding samples of a current picture by referenceto indicated samples in a reference picture where the current pictureand the reference picture are in different layers and hence havedifferent values of nuh_layer_id. For example, a picture in a lowerlayer N 631 can be used as a reference picture to code a correspondingpicture at a higher layer N+1 632. As a specific example, picture 611can be coded by reference to picture 615 according to inter-layerprediction 621. In such a case, the picture 615 is used as aninter-layer reference picture. An inter-layer reference picture is areference picture used for inter-layer prediction 621. In most cases,inter-layer prediction 621 is constrained such that a current picture,such as picture 611, can only use inter-layer reference picture(s) thatare included in the same AU 627 and that are at a lower layer, such aspicture 615. When multiple layers (e.g., more than two) are available,inter-layer prediction 621 can encode/decode a current picture based onmultiple inter-layer reference picture(s) at lower levels than thecurrent picture.

A video encoder can employ a multi-layer video sequence 600 to encodepictures 611-618 via many different combinations and/or permutations ofinter-prediction 623 and inter-layer prediction 621. For example,picture 615 may be coded according to intra-prediction. Pictures 616-618can then be coded according to inter-prediction 623 by using picture 615as a reference picture. Further, picture 611 may be coded according tointer-layer prediction 621 by using picture 615 as an inter-layerreference picture. Pictures 612-614 can then be coded according tointer-prediction 623 by using picture 611 as a reference picture. Assuch, a reference picture can serve as both a single layer referencepicture and an inter-layer reference picture for different codingmechanisms. By coding higher layer N+1 632 pictures based on lower layerN 631 pictures, the higher layer N+1 632 can avoid employingintra-prediction, which has much lower coding efficiency thaninter-prediction 623 and inter-layer prediction 621. As such, the poorcoding efficiency of intra-prediction can be limited to thesmallest/lowest quality pictures, and hence limited to coding thesmallest amount of video data. The pictures used as reference picturesand/or inter-layer reference pictures can be indicated in entries ofreference picture list(s) contained in a reference picture liststructure.

The pictures 611-618 may also be included in access units (AUs) 627. AnAU 627 is a set of coded pictures that are included in different layersand are associated with the same output time during decoding.Accordingly, coded pictures in the same AU 627 are scheduled for outputfrom a DPB at a decoder at the same time. For example, pictures 614 and618 are in the same AU 627. Pictures 613 and 617 are in a different AU627 from pictures 614 and 618. Pictures 614 and 618 in the same AU 627may be displayed in the alternative. For example, picture 618 may bedisplayed when a small picture size is desired and picture 614 may bedisplayed when a large picture size is desired. When the large picturesize is desired, picture 614 is output and picture 618 is used only forinter-layer prediction 621. In this case, picture 618 is discardedwithout being output once inter-layer prediction 621 is complete.

For conformance testing purposes, the AUs 627 may be further dividedinto DUs 628. A DU 628 can be defined as an AU 627 or a subset of an AU627 including one or more VCL NAL units in an AU 627 and associatednon-VCL NAL units. Stated differently, a DU 628 can contain a singlecoded picture along with syntax elements as desired to support decodingthe picture. In a single layer bitstream, a DU 628 is an AU 627. In amulti-layer bitstream, a DU 628 is a subset of an AU 627. Thedistinction between AUs 627 and DUs 628 may be employed when performingconformance tests at a HRD. For example, some conformance tests areconfigured to be applied to each AUs 627, while other conformance testsare configured to be applied to each DU 628 in each AU 627. Aconformance test that is applied to one or more entire AUs 627 can bereferred to as an AU level operation. A conformance test that is appliedto one or more DUs 628 can be referred to as a DU level operation.Accordingly, AU level is a description of an operation as being appliedto one or more entire AUs 627, and hence applied to one or more entiregroups of pictures sharing the same output time. Further, DU level is adescription of an operation as being applied to one or more entire DUs628, and hence that is applied to one or more pictures.

FIG. 7 is a schematic diagram illustrating an example bitstream 700. Forexample, the bitstream 700 can be generated by a codec system 200 and/oran encoder 300 for decoding by a codec system 200 and/or a decoder 400according to method 100. Further, the bitstream 700 may include amulti-layer video sequence 600. In addition, the bitstream 700 mayinclude various parameters to control the operation of a HRD, such asHRD 500. Based on such parameters, the HRD can check the bitstream 700for conformance with standards prior to transmission toward a decoderfor decoding.

The bitstream 700 includes a VPS 711, one or more SPSs 713, a pluralityof picture parameter sets (PPSs) 715, a plurality of slice headers 717,image data 720, a buffering period (BP) SEI message 716, a PT SEImessage 718 and/or a DUI SEI message 719. A VPS 711 contains datarelated to the entire bitstream 700. For example, the VPS 711 maycontain data related OLSs, layers, and/or sublayers used in thebitstream 700. An SPS 713 contains sequence data common to all picturesin a coded video sequence contained in the bitstream 700. For example,each layer may contain one or more coded video sequences, and each codedvideo sequence may reference a SPS 713 for corresponding parameters. Theparameters in a SPS 713 can include picture sizing, bit depth, codingtool parameters, bit rate restrictions, etc. It should be noted that,while each sequence refers to a SPS 713, a single SPS 713 can containdata for multiple sequences in some examples. The PPS 715 containsparameters that apply to an entire picture. Hence, each picture in thevideo sequence may refer to a PPS 715. It should be noted that, whileeach picture refers to a PPS 715, a single PPS 715 can contain data formultiple pictures in some examples. For example, multiple similarpictures may be coded according to similar parameters. In such a case, asingle PPS 715 may contain data for such similar pictures. The PPS 715can indicate coding tools available for slices in correspondingpictures, quantization parameters, offsets, etc.

The slice header 717 contains parameters that are specific to each slicein a picture. Hence, there may be one slice header 717 per slice 727 inthe video sequence. The slice header 717 may contain slice typeinformation, filtering information, prediction weights, tile entrypoints, deblocking parameters, etc. It should be noted that in someexamples, a bitstream 700 may also include a picture header, which is asyntax structure that contains parameters that apply to all slices 727in a single picture 725. For this reason, a picture header and a sliceheader 717 may be used interchangeably in some contexts. For example,certain parameters may be moved between the slice header 717 and apicture header depending on whether such parameters are common to allslices 727 in a picture 725.

The image data 720 contains video data encoded according tointer-prediction and/or intra-prediction as well as correspondingtransformed and quantized residual data. For example, the image data 720may include layers 723, pictures 725, and/or slices 727. A layer 723 isa set of VCL NAL units that share a specified characteristic (e.g., acommon resolution, frame rate, image size, etc.) as indicated by a layerID, such as a nuh_layer_id, and associated non-VCL NAL units. Forexample, a layer 723 may include a set of pictures 725 that share thesame nuh_layer_id as well as associated parameter sets and/or SEImessages. A layer 723 may be substantially similar to layers 631 and/or632. A nuh_layer_id is a syntax element that specifies an identifier ofa layer 723 that includes at least one NAL unit. For example, the lowestquality layer 723, known as a base layer, may include the lowest valueof nuh_layer_id with increasing values of nuh_layer_id for layers 723 ofhigher quality. Hence, a lower layer is a layer 723 with a smaller valueof nuh_layer_id and a higher layer is a layer 723 with a larger value ofnuh_layer_id. Layers 723 can also be included an OLS. An OLS is a set oflayers 723 for which one or more layers 723 are specified as an outputlayer(s). An output layer is any layer 723 that is designated for outputand display at a decoder. Layers 723 that are not output layers can beincluded in an OLS to support decoding an output layer, for example viainter-layer prediction.

A picture 725 is an array of luma samples and/or an array of chromasamples that create a frame or a field thereof. For example, a picture725 is a coded image that may be output for display or used to supportcoding of other picture(s) 725 for output. A picture 725 contains one ormore slices 727. A slice 727 may be defined as an integer number ofcomplete tiles or an integer number of consecutive complete coding treeunit (CTU) rows (e.g., within a tile) of a picture 725 that areexclusively contained in a single NAL unit. The slices 727 are furtherdivided into CTUs and/or coding tree blocks (CTBs). A CTU is a group ofsamples of a predefined size that can be partitioned by a coding tree. ACTB is a subset of a CTU and contains luma components or chromacomponents of the CTU. The CTUs/CTBs are further divided into codingblocks based on coding trees. The coding blocks can then beencoded/decoded according to prediction mechanisms.

A SEI message is a syntax structure with specified semantics thatconveys information that is not needed by the decoding process in orderto determine the values of the samples in decoded pictures. For example,the SEI messages may contain data to support HRD processes or othersupporting data that is not directly relevant to decoding the bitstream700 at a decoder. A BP SEI message 716 is a SEI message that containsHRD parameters for initializing a HRD to manage a CPB for testingcorresponding OLSs and/or layers 723. A PT SEI message 718 is a SEImessage that contains HRD parameters for managing delivery informationfor AUs at the CPB and/or the DPB for testing corresponding OLSs and/orlayers 723. A DUI SEI message 719 is a SEI message that contains HRDparameters for managing delivery information for DUs at the CPB and/orthe DPB for testing corresponding OLSs and/or layers 723.

It should be noted that the bitstream 700 can be coded as a sequence ofNAL units. A NAL unit is a container for video data and/or supportingsyntax. A NAL unit can be a VCL NAL unit or a non-VCL NAL unit. A VCLNAL unit is a NAL unit coded to contain video data. Specifically, a VCLNAL unit contains a slice 727 and an associated slice header 717. Anon-VCL NAL unit is a NAL unit that contains non-video data such assyntax and/or parameters that support decoding the video data,performance of conformance checking, or other operations. Non-VCL NALunits may include a VPS NAL unit, a SPS NAL unit, and a PPS NAL unit,which contain a VPS 711, a SPS 713, and a PPS 715, respectively. Thenon-VCL NAL unit may also include a SEI NAL unit that can contain a BPSEI message 716, a PT SEI message 718, and/or a DUI SEI message 719.Accordingly, an SEI NAL unit is a NAL unit that contains an SEI message.It should be noted that the preceding list of NAL units is exemplary andnot exhaustive.

A HRD, such as HRD 500, can be employed to check the bitstream 700 forconformance to standards. The HRD can employ HRD parameters to performconformance tests on the bitstream 700. HRD parameters 735 can be storedin a syntax structure in the VPS 711 and/or the SPS 713. HRD parameters735 are syntax elements that initialize and/or define operationalconditions of an HRD. The BP SEI message 716, PT SEI message 718, and/ora DUI SEI message 719 contain parameters that further define operationsof the HRD for particular sequences, AUs, and/or DUs based on the HRDparameters 735 in the VPS 711 and/or the SPS 713.

In some video coding systems, the BP SEI message 716, PT SEI message718, and/or a DUI SEI message 719 may contain parameters that directlyreference the VPS 711. This dependency creates certain difficulties. Forexample, the bitstream 700 may be encoded in various layers 723 and/orOLSs. When a decoder requests an OLS, the encoder, a slicer, and/or anintermediate storage server can transmit an OLS of the layers 723 to thedecoder based on decoder capabilities and/or based on current networkconditions. Specifically, the encoder, slicer, and/or storage serveremploys a bitstream extraction process to remove the layers 723 outsidethe OLS from the bitstream 700, and transmits the remaining layers 723toward the decoder. This process allows many different decoders to eachobtain different representations of the bitstream 700 based on decoderside conditions. As noted above, the VPS 711 contains data related tothe OLSs and/or layers 723. However, some OLSs contain a single layer723. When an OLS with a single layer 723 is transmitted to a decoder,the decoder may have no need for the data in the VPS 711 as the data inthe SPS 713, PPS 715, and slice headers 717 may be sufficient to decodea single layer 723 bitstream. In order to avoid transmitting unneededdata, the encoder, slicer, and/or storage server may remove the VPS 711as part of the bitstream extraction process. This approach may bebeneficial as this approach may increase the coding efficiency of thesub-bitstream that extracted and transmitted to the decoder. However,the dependency of the BP SEI message 716, PT SEI message 718, and/or aDUI SEI message 719 may create errors when the VPS 711 is removed.Specifically, omitting the VPS 711 can cause the SEI messages to returnan error as the data upon which they depend in the VPS 711 is notreceived at the decoder when the VPS 711 is removed. Further, the HRDchecks the bitstream for conformance by mimicking the decoder. As such,the HRD may check an OLS with a single layer 723 without parsing the VPS711. Accordingly, the HRD in some systems may be unable to resolve theparameters in the BP SEI message 716, the PT SEI message 718, and/or theDUI SEI message 719, and hence the HRD may be unable to check such OLSsfor conformance.

Bitstream 700 is improved to correct the problems described above.Specifically, parameters are added to the BP SEI message 716, PT SEImessage 718, and/or a DUI SEI message 719 to remove the dependency onthe VPS 711. Accordingly, the BP SEI message 716, PT SEI message 718,and/or a DUI SEI message 719 can be completely parsed and resolved bythe HRD and/or decoder even when the VPS 711 is omitted for OLSs thatinclude a single layer 723. The dependency may be removed by including adu_hrd_params_present_flag 731 and adu_cpb_params_in_pic_timing_sei_flag 733 in one or more of the SEImessages. In the example shown, the du_hrd_params_present_flag 731 andthe du_cpb_params_in_pic_timing_sei_flag 733 are included in the BP SEImessage 716.

The du_hrd_params_present_flag 731 is a syntax element that specifieswhether the HRD should operate on an AU level or a DU level. An AU levelis a description of an operation as being applied to one or more entireAUs (e.g., applied to one or more entire groups of pictures sharing thesame output time). A DU level is a description of an operation as beingapplied to one or more entire DUs (e.g., applied to one or morepictures). In a specific example, the du_hrd_params_present_flag 731 isset to one when specifying that DU level HRD parameters are present andthe HRD can be operated at the AU level or the DU level, and is set tozero when specifying that DU level HRD parameters are not present andthe HRD operates at the AU level.

When the HRD operates at the DU level (e.g., whendu_hrd_params_present_flag 731 is set to one), the HRD should refer toDU parameters, such as a CPB removal delay 737. The CPB removal delay737 is a syntax element that specifies a CPB removal delay for DUs,which is an amount time that one or more DUs (pictures 725) may remainin a CPB prior to transfer to a DPB in a HRD. However, the relevant CPBremoval delay 737 may be included in the PT SEI message 718, or the DUISEI message 719, depending on the example. Thedu_cpb_params_in_pic_timing_sei_flag 733 is a syntax element thatspecifies whether DU level CPB removal delay 737 parameters are presentin the PT SEI message 718 or the DUI SEI message 719. In a specificexample, the du_cpb_params_in_pic_timing_sei_flag 733 is set to one whenspecifying that that DU level CPB removal delay 737 parameters arepresent in a PT SEI message 718 and no DUI SEI message 719 is available.Further, the du_cpb_params_in_pic_timing_sei_flag 733 can be set to zerowhen specifying that DU level CPB removal delay 737 parameters arepresent in a DUI SEI message 719 and PT SEI messages 718 do not includeDU level CPB removal delay 737 parameters.

By including the du_hrd_params_present_flag 731 and thedu_cpb_params_in_pic_timing_sei_flag 733 in the SEI messages, the SEImessages do not depend on the VPS 711. Hence, the BP SEI message 716,the PT SEI message 718, and/or the DUI SEI message 719 can be parsedeven when the VPS 711 is omitted from the bitstream 700. Accordingly,the HRD can properly parse the BP SEI message 716, the PT SEI message718, and/or the DUI SEI message 719 and perform conformance tests onOLSs with a single layer. Further, the decoder can parse and use thesyntax elements in the BP SEI message 716, the PT SEI message 718,and/or the DUI SEI message 719 as desired to support decoding processes.As a result, the functionality of the encoder and the decoder isincreased and errors are avoided. Further, removing the dependencybetween the SEI messages and the VPS 711 supports removal of the VPS 711in certain cases, which increases coding efficiency, and hence reducesprocessor, memory, and/or network signaling resource usage at both theencoder and the decoder in such cases.

The preceding information is now described in more detail herein below.Layered video coding is also referred to as scalable video coding orvideo coding with scalability. Scalability in video coding may besupported by using multi-layer coding techniques. A multi-layerbitstream comprises a base layer (BL) and one or more enhancement layers(ELs). Example of scalabilities includes spatial scalability,quality/signal to noise ratio (SNR) scalability, multi-view scalability,frame rate scalability, etc. When a multi-layer coding technique isused, a picture or a part thereof may be coded without using a referencepicture (intra-prediction), may be coded by referencing referencepictures that are in the same layer (inter-prediction), and/or may becoded by referencing reference pictures that are in other layer(s)(inter-layer prediction). A reference picture used for inter-layerprediction of the current picture is referred to as an inter-layerreference picture (ILRP). FIG. 6 illustrates an example of multi-layercoding for spatial scalability in which pictures in different layershave different resolutions.

Some video coding families provide support for scalability in separatedprofile(s) from the profile(s) for single-layer coding. Scalable videocoding (SVC) is a scalable extension of the advanced video coding (AVC)that provides support for spatial, temporal, and quality scalabilities.For SVC, a flag is signaled in each macroblock (MB) in EL pictures toindicate whether the EL MB is predicted using the collocated block froma lower layer. The prediction from the collocated block may includetexture, motion vectors, and/or coding modes. Implementations of SVC maynot directly reuse unmodified AVC implementations in their design. TheSVC EL macroblock syntax and decoding process differs from the AVCsyntax and decoding process.

Scalable HEVC (SHVC) is an extension of HEVC that provides support forspatial and quality scalabilities. Multiview HEVC (MV-HEVC) is anextension of HEVC that provides support for multi-view scalability. 3DHEVC (3D-HEVC) is an extension of HEVC that provides support for 3Dvideo coding that is more advanced and more efficient than MV-HEVC.Temporal scalability may be included as an integral part of asingle-layer HEVC codec. In the multi-layer extension of HEVC, decodedpictures used for inter-layer prediction come only from the same AU andare treated as long-term reference pictures (LTRPs). Such pictures areassigned reference indices in the reference picture list(s) along withother temporal reference pictures in the current layer. Inter-layerprediction (ILP) is achieved at the prediction unit level by setting thevalue of the reference index to refer to the inter-layer referencepicture(s) in the reference picture list(s). Spatial scalabilityresamples a reference picture or part thereof when an ILRP has adifferent spatial resolution than the current picture being encoded ordecoded. Reference picture resampling can be realized at either picturelevel or coding block level.

VVC may also support layered video coding. A VVC bitstream can includemultiple layers. The layers can be all independent from each other. Forexample, each layer can be coded without using inter-layer prediction.In this case, the layers are also referred to as simulcast layers. Insome cases, some of the layers are coded using ILP. A flag in the VPScan indicate whether the layers are simulcast layers or whether somelayers use ILP. When some layers use ILP, the layer dependencyrelationship among layers is also signaled in the VPS. Unlike SHVC andMV-HEVC, VVC may not specify OLSs. An OLS includes a specified set oflayers, where one or more layers in the set of layers are specified tobe output layers. An output layer is a layer of an OLS that is output.In some implementations of VVC, only one layer may be selected fordecoding and output when the layers are simulcast layers. In someimplementations of VVC, the entire bitstream including all layers isspecified to be decoded when any layer uses ILP. Further, certain layersamong the layers are specified to be output layers. The output layersmay be indicated to be only the highest layer, all the layers, or thehighest layer plus a set of indicated lower layers.

The preceding aspects contain certain problems. For example, thenuh_layer_id values for SPS, PPS, and APS NAL units may not be properlyconstrained. Further, the TemporalId value for SEI NAL units may not beproperly constrained. In addition, setting of NoOutputOfPriorPicsFlagmay not be properly specified when reference picture resampling isenabled and pictures within a CLVS have different spatial resolutions.Also, in some video coding systems suffix SEI messages cannot becontained in a scalable nesting SEI message. As another example,buffering period, picture timing, and decoding unit information SEImessages may include parsing dependencies on VPS and/or SPS.

In general, this disclosure describes video coding improvementapproaches. The descriptions of the techniques are based on VVC.However, the techniques also apply to layered video coding based onother video codec specifications.

One or more of the abovementioned problems may be solved as follows. Thenuh_layer_id values for SPS, PPS, and APS NAL units are properlyconstrained herein. The TemporalId value for SEI NAL units is properlyconstrained herein. Setting of the NoOutputOfPriorPicsFlag is properlyspecified when reference picture resampling is enabled and pictureswithin a CLVS have different spatial resolutions. Suffix SEI messagesare allowed to be contained in a scalable nesting SEI message. Parsingdependencies of BP, PT, and DUI SEI messages on VPS or SPS may beremoved by repeating the syntax elementdecoding_unit_hrd_params_present_flag in the BP SEI message syntax, thesyntax elements decoding_unit_hrd_params_present_flag anddecoding_unit_cpb_params_in_pic_timing_sei_flag in the PT SEI messagesyntax, and the syntax elementdecoding_unit_cpb_params_in_pic_timing_sei_flag in the DUI SEI message.

An example implementation of the preceding mechanisms is as follows. Anexample general NAL unit semantics is as follows.

A nuh_temporal_id_plus1 minus 1 specifies a temporal identifier for theNAL unit. The value of nuh_temporal_id_plus1 should not be equal tozero. The variable TemporalId may be derived as follows:

TemporalId=nuh_temporal_id_plus1−1

When nal_unit_type is in the range of IDR_W_RADL to RSV_IRAP_13,inclusive, TemporalId should be equal to zero. When nal_unit_type isequal to STSA_NUT, TemporalId should not be equal to zero.

The value of TemporalId should be the same for all VCL NAL units of anaccess unit. The value of TemporalId of a coded picture, a layer accessunit, or an access unit may be the value of the TemporalId of the VCLNAL units of the coded picture, the layer access unit, or the accessunit. The value of TemporalId of a sub-layer representation may be thegreatest value of TemporalId of all VCL NAL units in the sub-layerrepresentation.

The value of TemporalId for non-VCL NAL units is constrained as follows.If nal_unit_type is equal to DPS NUT, VPS NUT, or SPS NUT, TemporalId isequal to zero and the TemporalId of the access unit containing the NALunit should be equal to zero. Otherwise if nal_unit_type is equal toEOS_NUT or EOB NUT, TemporalId should be equal to zero. Otherwise, ifnal_unit_type is equal to AUD_NUT, FD_NUT, PREFIX_SEI_NUT, orSUFFIX_SEI_NUT, TemporalId should be equal to the TemporalId of theaccess unit containing the NAL unit. Otherwise, when nal_unit_type isequal to PPS_NUT or APS_NUT, TemporalId should be greater than or equalto the TemporalId of the access unit containing the NAL unit. When theNAL unit is a non-VCL NAL unit, the value of TemporalId should be equalto the minimum value of the TemporalId values of all access units towhich the non-VCL NAL unit applies. When nal_unit_type is equal toPPS_NUT or APS_NUT, TemporalId may be greater than or equal to theTemporalId of the containing access unit. This is because all PPSs andAPSs may be included in the beginning of a bitstream. Further, the firstcoded picture has TemporalId equal to zero.

An example sequence parameter set RBSP semantics is as follows. An SPSRBSP should be available to the decoding process prior to beingreferenced. The SPS may be included in at least one access unit withTemporalId equal to zero or provided through external mechanism. The SPSNAL unit containing the SPS may be constrained to have a nuh_layer_idequal to the lowest nuh_layer_id value of PPS NAL units that refer tothe SPS.

An example picture parameter set RBSP semantics is as follows. A PPSRBSP should be available to the decoding process prior to beingreferenced. The PPS should be included in at least one access unit withTemporalId less than or equal to the TemporalId of the PPS NAL unit orprovided through external mechanism. The PPS NAL unit containing the PPSRBSP should have a nuh_layer_id equal to the lowest nuh_layer_id valueof the coded slice NAL units that refer to the PPS.

An example adaptation parameter set semantics is as follows. Each APSRBSP should be available to the decoding process prior to beingreferenced. The APS should also be included in at least one access unitwith TemporalId less than or equal to the TemporalId of the coded sliceNAL unit that refers the APS or provided through an external mechanism.An APS NAL unit is allowed to be shared by pictures/slices of multiplelayers. The nuh_layer_id of an APS NAL unit should be equal to thelowest nuh_layer_id value of the coded slice NAL units that refer to theAPS NAL unit. Alternatively, an APS NAL unit may not be shared bypictures/slices of multiple layers. The nuh_layer_id of an APS NAL unitshould be equal to the nuh_layer_id of slices referring to the APS.

In an example, removal of pictures from the DPB before decoding of thecurrent picture is discussed as follows. The removal of pictures fromthe DPB before decoding of the current picture (but after parsing theslice header of the first slice of the current picture) may occur at theCPB removal time of the first decoding unit of access unit n (containingthe current picture). This proceeds as follows. The decoding process forreference picture list construction is invoked and the decoding processfor reference picture marking is invoked.

When the current picture is a coded layer video sequence start (CLVSS)picture that is not picture zero, the following ordered steps areapplied. The variable NoOutputOfPriorPicsFlag is derived for the decoderunder test as follows. If the value of pic_width_max_in_luma_samples,pic_height_max_in_luma_samples, chroma_format_idc,separate_colour_plane_flag, bit_depth_luma_minus8,bit_depth_chroma_minus8 or sps_max_decpic_buffering_minus1[Htid] derivedfrom the SPS is different from the value of pic_width_in_luma_samples,pic_height_in_luma_samples, chroma_format_idc,separate_colour_plane_flag, bit_depth_luma_minus8,bit_depth_chroma_minus8 or sps_max_decpic_buffering_minus1[Htid],respectively, derived from the SPS referred to by the preceding picture,NoOutputOfPriorPicsFlag may be set to one by the decoder under test,regardless of the value of no_output_of_prior_pics_flag. It should benoted that, although setting NoOutputOfPriorPicsFlag equal tono_output_of_prior_pics_flag may be preferred under these conditions,the decoder under test is allowed to set NoOutputOfPriorPicsFlag to onein this case. Otherwise, NoOutputOfPriorPicsFlag may be set equal tono_output_of_prior_pics_flag.

The value of NoOutputOfPriorPicsFlag derived for the decoder under testis applied for the HRD, such that when the value ofNoOutputOfPriorPicsFlag is equal to 1, all picture storage buffers inthe DPB are emptied without output of the pictures they contain, and theDPB fullness is set equal to zero. When both of the following conditionsare true for any pictures k in the DPB, all such pictures k in the DPBare removed from the DPB. Picture k is marked as unused for reference,and picture k has PictureOutputFlag equal to zero or a corresponding DPBoutput time is less than or equal to the CPB removal time of the firstdecoding unit (denoted as decoding unit m) of the current picture n.This may occur when DpbOutputTime[k] is less than or equal toDuCpbRemovalTime[m]. For each picture that is removed from the DPB, theDPB fullness is decremented by one.

In an example, output and removal of pictures from the DPB is discussedas follows. The output and removal of pictures from the DPB before thedecoding of the current picture (but after parsing the slice header ofthe first slice of the current picture) may occur when the firstdecoding unit of the access unit containing the current picture isremoved from the CPB and proceeds as follows. The decoding process forreference picture list construction and decoding process for referencepicture marking are invoked.

If the current picture is a CLVSS picture that is not picture zero, thefollowing ordered steps are applied. The variableNoOutputOfPriorPicsFlag can be derived for the decoder under test asfollows. If the value of pic_width_max_in_luma_samples,pic_height_max_in_luma_samples, chroma_format_idc,separate_colour_plane_flag, bit_depth_luma_minus8,bit_depth_chroma_minus8 or sps_max_dec_pic_buffering_minus1[Htid]derived from the SPS is different from the value ofpic_width_in_luma_samples, pic_height_in_luma_samples,chroma_format_idc, separate_colour_plane_flag, bit_depth_luma_minus8,bit_depth_chroma_minus8 or sps_max_dec_pic_buffering_minus1[Htid],respectively, derived from the SPS referred to by the preceding picture,NoOutputOfPriorPicsFlag may be set to one by the decoder under test,regardless of the value of no_output_of_prior_pics_flag. It should benoted that although setting NoOutputOfPriorPicsFlag equal tono_output_of_prior_pics_flag is preferred under these conditions, thedecoder under test can set NoOutputOfPriorPicsFlag to one in this case.Otherwise, NoOutputOfPriorPicsFlag can be set equal tono_output_of_prior_pics_flag.

The value of NoOutputOfPriorPicsFlag derived for the decoder under testcan be applied for the HRD as follows. If NoOutputOfPriorPicsFlag isequal to one, all picture storage buffers in the DPB are emptied withoutoutput of the pictures they contain and the DPB fullness is set equal tozero. Otherwise (NoOutputOfPriorPicsFlag is equal to zero), all picturestorage buffers containing a picture that is marked as not needed foroutput and unused for reference are emptied (without output) and allnon-empty picture storage buffers in the DPB are emptied by repeatedlyinvoking a bumping process and the DPB fullness is set equal to zero.

Otherwise (the current picture is not a CLVSS picture), all picturestorage buffers containing a picture which are marked as not needed foroutput and unused for reference are emptied (without output). For eachpicture storage buffer that is emptied, the DPB fullness is decrementedby one. When one or more of the following conditions are true, thebumping process is invoked repeatedly while further decrementing the DPBfullness by one for each additional picture storage buffer that isemptied until none of the following conditions are true. A condition isthat the number of pictures in the DPB that are marked as needed foroutput is greater than sps_max_num_reorder_pics[Htid]. Another conditionis that a sps_max_latency_increase_plus1[Htid] is not equal to zero andthere is at least one picture in the DPB that is marked as needed foroutput for which the associated variable PicLatencyCount is greater thanor equal to SpsMaxLatencyPictures[Htid]. Another condition is that thenumber of pictures in the DPB is greater than or equal toSubDpbSize[Htid].

An example general SEI message syntax is as follows.

sei_payload( payloadType, payloadSize ) { Descriptor  if( nal_unit_type= = PREFIX_SEI_NUT )   if( payloadType = = 0 )    buffering_period(payloadSize )   else if( payloadType = = 1 )    pic_timing( payloadSize)   else if( payloadType = = 3 )    filler_payload( payloadSize )   elseif( payloadType = = 130 )    decoding_unit_info( payloadSize )   elseif( payloadType = = 133 )    scalable_nesting( payloadSize )   else if(payloadType = = 145 )   dependent_rap_indication( payloadSize )     //Specified in ITU-T H.SEI | ISO/IEC 23002-7.   else if( payloadType = =168 )    frame_field_info( payloadSize )   else    reserved_sei_message(payloadSize )  else /* nal_unit_type = = SUFFIX_SEI_NUT */   if(payloadType = = 3 )    filler_payload( payloadSize )   if( payloadType == 132 )    decoded_picture_hash( payloadSize )     // Specified in ITU-TH.SEI | ISO/IEC 23002-7.   else if( payloadType = = 133 )   scalable_nesting( payloadSize )   else    reserved_sei_message(payloadSize )  if( more_data_in_payload( ) ) {   if(payload_extension_present( ) )    reserved_payload_extension_data u(v)  payload_bit_equal_to_one /* equal to 1 */ f(1)   while( !byte_aligned())    payload_bit_equal_to_zero /* equal to 0 */ f(1)  } }

An example scalable nesting SEI message syntax is as follows.

scalable_nesting( payloadSize ) { Descriptor  nesting_ols_flag u(1)  if(nesting_ols_flag ) {   nesting_num_olss_minus1 ue(v)   for( i = 0; i <=nesting_num_olss_minus1; i++ ) {    nesting_ols_idx_delta_minus1[ i ]ue(v)    if( NumLayersInOls[ NestingOlsIdx[ i ] ] > 1 ) {    nesting_num_ols_layers_minus1[ i ] ue(v)     for( j = 0; j <=nesting_num_ols_layers_minus1[ i ]; j++ )     nesting_ols_layer_idx_delta_minus1[ i ][ j ] ue(v)    }   }  } else{   nesting_all_layers_flag u(1)   if( !nesting_all_layers_flag ) {   nesting_num_layers_minus1 ue(v)    for( i = 1; i <=nesting_num_layers_minus1; i++ )     nesting_layer_id[ i ] u(6)   }  } nesting_num_seis_minus1 ue(v)  while( !byte_aligned( ))  nesting_zero_bit /* equal to 0 */ u(1)  for( i = 0; i <=nesting_num_seis_minus1; i++ )   sei_message( ) }

An example scalable nesting SEI message semantics is as follows. Ascalable nesting SEI message provides a mechanism to associate SEImessages with specific layers in the context of specific OLSs or withspecific layers not in the context of an OLS. A scalable nesting SEImessage contains one or more SEI messages. The SEI messages contained inthe scalable nesting SEI message are also referred to as thescalable-nested SEI messages. Bitstream conformance may require that thefollowing restrictions apply when SEI messages are contained in ascalable nesting SEI message.

An SEI message that has payloadType equal to one hundred thirty-two(decoded picture hash) or one hundred thirty-three (scalable nesting)should not be contained in a scalable nesting SEI message. When ascalable nesting SEI message contains a buffering period, picturetiming, or decoding unit information SEI message, the scalable nestingSEI message should not contain any other SEI message with payloadTypenot equal to zero (buffering period), one (picture timing), or onehundred thirty (decoding unit information).

Bitstream conformance may also require that the following restrictionsapply on the value of the nal_unit_type of the SEI NAL unit containing ascalable nesting SEI message. When a scalable nesting SEI messagecontains an SEI message that has payloadType equal to zero (bufferingperiod), one (picture timing), one hundred thirty (decoding unitinformation), one hundred forty five (dependent RAP indication), or onehundred sixty eight (frame-field information), the SEI NAL unitcontaining the scalable nesting SEI message should have a nal_unit_typeset equal to PREFIX_SEI_NUT. When a scalable nesting SEI messagecontains an SEI message that has payloadType equal to one hundredthirty-two (decoded picture hash), the SEI NAL unit containing thescalable nesting SEI message should have a nal_unit_type set equal toSUFFIX_SEI_NUT.

A nesting_ols_flag may be set equal to one to specify that thescalable-nested SEI messages apply to specific layers in the context ofspecific OLSs. The nesting_ols_flag may be set equal to zero to specifythat that the scalable-nested SEI messages generally apply (e.g., not inthe context of an OLS) to specific layers.

Bitstream conformance may require that the following restrictions areapplied to the value of nesting_ols_flag. When the scalable nesting SEImessage contains an SEI message that has payloadType equal to zero(buffering period), one (picture timing), or one hundred thirty(decoding unit information), the value of nesting_ols_flag should beequal to one. When the scalable nesting SEI message contains an SEImessage that has payloadType equal to a value in VclAssociatedSeiList,the value of nesting_ols_flag should be equal to zero.

A nesting_num_olss_minus1 plus one specifies the number of OLSs to whichthe scalable-nested SEI messages apply. The value ofnesting_num_olss_minus1 should be in the range of zero toTotalNumOlss−1, inclusive. The nesting_ols_idx_delta_minus1[i] is usedto derive the variable NestingOlsIdx[i] that specifies the OLS index ofthe i-th OLS to which the scalable-nested SEI messages apply whennesting_ols_flag is equal to one. The value ofnesting_ols_idx_delta_minus1[i] should be in the range of zero toTotalNumOlss−2, inclusive.

The variable NestingOlsIdx[i] may be derived as follows:

if( i == 0 )  NestingOlsIdx[ i ] = nesting_ols_idx_delta_minus1[ i ]else  NestingOlsIdx[ i ] = NestingOlsIdx[ i − 1 ] +nesting_ols_idx_delta_minus1[ i ] + 1

The nesting_num_ols_layers_minus1[i] plus one specifies the number oflayers to which the scalable-nested SEI messages apply in the context ofthe NestingOlsIdx[i]-th OLS. The value ofnesting_num_ols_layers_minus1[i] should be in the range of zero toNumLayersInOls[NestingOlsIdx[i]]−1, inclusive.

The nesting_ols_layer_idx_delta_minus1[i][j] is used to derive thevariable NestingOlsLayerIdx[i][j] that specifies the OLS layer index ofthe j-th layer to which the scalable-nested SEI messages apply in thecontext of the NestingOlsIdx[i]-th OLS when nesting_ols_flag is equal toone. The value of nesting_ols_layer_idx_delta_minus1[i] should be in therange of zero to NumLayersInOls[nestingOlsIdx[i]]−two, inclusive.

The variable NestingOlsLayerIdx[i][j] may be derived as follows:

if( j == 0 )  NestingOlsLayerIdx[ i ][ j ] =nesting_ols_layer_idx_delta_minus1[ i ][ j ] else  NestingOlsLayerIdx[ i][ j ] = NestingOlsLayerIdx[ i ][ j − 1 ] +  nesting_ols_layer_idx_delta_minus1[ i ][ j ] + 1

The lowest value among all values ofLayerIdInOls[NestingOlsIdx[i]][NestingOlsLayerIdx[i][0]] for i in therange of zero to nesting_num_olss_minus1, inclusive, should be equal tonuh_layer_id of the current SEI NAL unit (e.g., the SEI NAL unitcontaining the scalable nesting SEI message). Thenesting_all_layers_flag may be set equal to one to specify that thescalable-nested SEI messages generally apply to all layers that havenuh_layer_id greater than or equal to the nuh_layer_id of the currentSEI NAL unit. The nesting_all_layers_flag may be set equal to zero tospecify that the scalable-nested SEI messages may or may not generallyapply to all layers that have nuh_layer_id greater than or equal to thenuh_layer_id of the current SEI NAL unit.

The nesting_num_layers_minus1 plus one specifies the number of layers towhich the scalable-nested SEI messages generally apply. The value ofnesting_num_layers_minus1 should be in the range of zero tovps_max_layers_minus1−GeneralLayerIdx[nuh_layer_id], inclusive, wherenuh_layer_id is the nuh_layer_id of the current SEI NAL unit. Thenesting_layer_id[i] specifies the nuh_layer_id value of the i-th layerto which the scalable-nested SEI messages generally apply whennesting_all_layers_flag is equal to zero. The value ofnesting_layer_id[i] should be greater than nuh_layer_id, wherenuh_layer_id is the nuh_layer_id of the current SEI NAL unit.

When the nesting_ols_flag is equal to one, the variableNestingNumLayers, specifying the number of layer to which thescalable-nested SEI messages generally apply, and the listNestingLayerId[i] for i in the range of zero to NestingNumLayers−1,inclusive, specifying the list of nuh_layer_id value of the layers towhich the scalable-nested SEI messages generally apply, are derived asfollows, where nuh_layer_id is the nuh_layer_id of the current SEI NALunit:

if( nesting_all_layers_flag ) {  NestingNumLayers =vps_max_layers_minus1 + 1 − GeneralLayerIdx[ nuh_layer_id ]  for( i = 0;i < NestingNumLayers; i ++)   NestingLayerId[ i ] = vps_layer_id[GeneralLayerIdx[ nuh_layer_id ] + i ] (D-2) } else {  NestingNumLayers =nesting_num_layers_minus1 + 1  for( i = 0; i < NestingNumLayers; i ++)  NestingLayerId[ i ] = ( i == 0 ) ? nuh_layer_id : nesting_layer_id[ i] }

The nesting_num_seis_minus1 plus one specifies the number ofscalable-nested SEI messages. The value of nesting_num_seis_minus1should be in the range of zero to sixty three, inclusive. Thenesting_zero_bit should be set equal to zero.

FIG. 8 is a schematic diagram of an example video coding device 800. Thevideo coding device 800 is suitable for implementing the disclosedexamples/embodiments as described herein. The video coding device 800comprises downstream ports 820, upstream ports 850, and/or transceiverunits (Tx/Rx) 810, including transmitters and/or receivers forcommunicating data upstream and/or downstream over a network. The videocoding device 800 also includes a processor 830 including a logic unitand/or central processing unit (CPU) to process the data and a memory832 for storing the data. The video coding device 800 may also compriseelectrical, optical-to-electrical (OE) components, electrical-to-optical(EO) components, and/or wireless communication components coupled to theupstream ports 850 and/or downstream ports 820 for communication of datavia electrical, optical, or wireless communication networks. The videocoding device 800 may also include input and/or output (I/O) devices 860for communicating data to and from a user. The I/O devices 860 mayinclude output devices such as a display for displaying video data,speakers for outputting audio data, etc. The I/O devices 860 may alsoinclude input devices, such as a keyboard, mouse, trackball, etc.,and/or corresponding interfaces for interacting with such outputdevices.

The processor 830 is implemented by hardware and software. The processor830 may be implemented as one or more CPU chips, cores (e.g., as amulti-core processor), field-programmable gate arrays (FPGAs),application specific integrated circuits (ASICs), and digital signalprocessors (DSPs). The processor 830 is in communication with thedownstream ports 820, Tx/Rx 810, upstream ports 850, and memory 832. Theprocessor 830 comprises a coding module 814. The coding module 814implements the disclosed embodiments described herein, such as methods100, 900, and 1000, which may employ a multi-layer video sequence 600and/or a bitstream 700. The coding module 814 may also implement anyother method/mechanism described herein. Further, the coding module 814may implement a codec system 200, an encoder 300, a decoder 400, and/ora HRD 500. For example, the coding module 814 may be employed signaland/or read various parameters as described herein. Further, the codingmodule may be employed to encode and/or decode a video sequence based onsuch parameters. As such, the signaling changes described herein mayincrease the efficiency and/or avoid errors in the coding module 814.Accordingly, the coding module 814 may be configured to performmechanisms to address one or more of the problems discussed above.Hence, coding module 814 causes the video coding device 800 to provideadditional functionality and/or coding efficiency when coding videodata. As such, the coding module 814 improves the functionality of thevideo coding device 800 as well as addresses problems that are specificto the video coding arts. Further, the coding module 814 effects atransformation of the video coding device 800 to a different state.Alternatively, the coding module 814 can be implemented as instructionsstored in the memory 832 and executed by the processor 830 (e.g., as acomputer program product stored on a non-transitory medium).

The memory 832 comprises one or more memory types such as disks, tapedrives, solid-state drives, read only memory (ROM), random access memory(RAM), flash memory, ternary content-addressable memory (TCAM), staticrandom-access memory (SRAM), etc. The memory 832 may be used as anover-flow data storage device, to store programs when such programs areselected for execution, and to store instructions and data that are readduring program execution.

FIG. 9 is a flowchart of an example method 900 of encoding a videosequence into a bitstream, such as bitstream 700, by employing a SEImessage that may not depend on a VPS. Method 900 may be employed by anencoder, such as a codec system 200, an encoder 300, and/or a videocoding device 800 when performing method 100. Further, the method 900may operate on a HRD 500 and hence may perform conformance tests on amulti-layer video sequence 600.

Method 900 may begin when an encoder receives a video sequence anddetermines to encode that video sequence into a multi-layer bitstream,for example based on user input. At step 901, the encoder encodes aplurality of coded pictures into a bitstream. For example, the codedpictures can be organized into layers to create a multi-layer bitstream.Further, each coded picture can be included in a DU. The coded picturescan also be included in AUs, where an AU contains a set of pictures fromdifferent layers that have the same output time. A layer may include aset of VCL NAL units with the same layer ID and associated non-VCL NALunits. For example, the set of VCL NAL units are part of a layer whenthe set of VCL NAL units all have a particular value of nuh_layer_id. Alayer may include a set of VCL NAL units, where each VCL NAL unitcontains a slice of an encoded picture. The layer may also contain anyparameter sets used to code such pictures where such parameters areincluded in non-VCL NAL units. The layers may be included in one or moreOLSs. One or more of the layers may be output layers (e.g., each OLScontains at least one output layer). Layers that are not an output layerare encoded to support reconstructing the output layer(s), but suchsupporting layers are not intended for output at a decoder. In this way,the encoder can encode various combinations of layers for transmissionto a decoder upon request. The layer can be transmitted as desired toallow the decoder to obtain different representations of the videosequence depending on network conditions, hardware capabilities, and/oruser settings.

At step 903, the encoder can encode a current SEI message into thebitstream. The current SEI message may be a BP SEI message, a PT SEImessage, or a DUI SEI message, depending on the example. The current SEImessage comprises a du_hrd_params_present_flag that specifies whether DUlevel HRD parameters are present in the bitstream. Thedu_hrd_params_present_flag can further specify whether a HRD operates atan AU level or a DU level. An AU level indicates that HRD processes areapplied to entire AUs and a DU level indicates that HRD processes areapplied to individual DUs. As such, the du_hrd_params_present_flag canspecify a granularity of conformance tests (e.g., AU granularity or DUgranularity). In a specific example, the du_hrd_params_present_flag canbe set to one when specifying that DU level HRD parameters are presentand the HRD can be operated at the AU level or the DU level. Further,the du_hrd_params_present_flag can be set to zero when specifying thatDU level HRD parameters are not present and the HRD operates at the AUlevel.

The current SEI message may also include adu_cpb_params_in_pic_timing_sei_flag that specifies whether DU level CPBremoval delay parameters are present in a PT SEI message. Thedu_cpb_params_in_pic_timing_sei_flag may further specify whether DUlevel CPB removal delay parameters are present in a DUI SEI message. Ina specific example, the du_cpb_params_in_pic_timing_sei_flag can be setto one when specifying that the DU level CPB removal delay parametersare present in a PT SEI message and no DUI SEI message is available.Further, the du_cpb_params_in_pic_timing_sei_flag can be set to zerowhen specifying that DU level CPB removal delay parameters are presentin a DUI SEI message and PT SEI messages do not include DU level CPBremoval delay parameters. The preceding constraints and/or requirementsensure that the bitstream conforms with, for example, VVC or some otherstandard, modified as indicated herein. However, the encoder may also becapable of operating in other modes where it is not so constrained, suchas when operating under a different standard or a different version ofthe same standard.

At step 905, an HRD can perform a set of bitstream conformance tests onthe bitstream based on the current SEI message. For example, the HRD canread the du_hrd_params_present_flag to determine whether to test thebitstream at the AU level or whether DU parameters are present whichwould allow for testing at the DU level as well. Further, the HRD canread the du_cpb_params_in_pic_timing_sei_flag to determine whether theDU parameters, if present, can be found in a DUI SEI message or a PT SEImessage. The HRD can then obtain the desired parameters from theindicated SEI messages and perform the conformance tests based on thoseparameters. Based on the forgoing flags, the current SEI message doesnot depend on a VPS. As such, the current SEI message can be completelyparsed and resolved even when a VPS is not available. Accordingly, theconformance tests operate properly even when testing is performed on anOLS with a single layer and hence a VPS is not available to the HRD asthe VPS is not configured for transmission as part of the OLS.

At step 907, the encoder can store the bitstream for communicationtoward a decoder upon request. The encoder can also transmit thebitstream toward the decoder as desired.

FIG. 10 is a flowchart of an example method 1000 of decoding a videosequence from a bitstream, such as bitstream 700, that employs a SEImessage that may not depend on a VPS. Method 1000 may be employed by adecoder, such as a codec system 200, a decoder 400, and/or a videocoding device 800 when performing method 100. Further, method 1000 maybe employed on a multi-layer video sequence 600 that has been checkedfor conformance by a HRD, such as HRD 500.

Method 1000 may begin when a decoder begins receiving a bitstream ofcoded data representing a multi-layer video sequence, for example as aresult of method 900 and/or in response to a request by the decoder. Atstep 1001, the decoder receives a bitstream comprising a coded picturein one or more VCL NAL units. For example, the bitstream may include oneor more layers including the coded picture. Further, each coded picturecan be included in a DU. The coded pictures can also be included in AUs,where an AU contains a set of pictures from different layers that havethe same output time. A layer may include a set of VCL NAL units withthe same layer ID and associated non-VCL NAL units. For example, the setof VCL NAL units are part of a layer when the set of VCL NAL units allhave a particular value of nuh_layer_id. A layer may include a set ofVCL NAL units where each VCL NAL unit contain a slice of a codedpicture. The layer may also contain any parameter sets used to code suchpictures where such parameters are included in non-VCL NAL units. Thelayers may be included in an OLS. One or more of the layers may beoutput layers. Layers that are not an output layer are encoded tosupport reconstructing the output layer(s), but such supporting layersare not intended for output. In this way, the decoder can obtaindifferent representations of the video sequence depending on networkconditions, hardware capabilities, and/or user settings.

The bitstream also comprises a current SEI message. The current SEImessage may be a BP SEI message, a PT SEI message, or a DUI SEI message,depending on the example. The current SEI message comprises adu_hrd_params_present_flag that specifies whether DU level HRDparameters are present in the bitstream. The du_hrd_params_present_flagcan further specify whether a HRD at the encoder operates at an AU levelor a DU level. An AU level indicates that HRD processes are applied toentire AUs and a DU level indicates that HRD processes are applied toindividual DUs. As such, the du_hrd_params_present_flag can specify agranularity of conformance tests (e.g., AU granularity or DUgranularity). In a specific example, the du_hrd_params_present_flag canbe set to one when specifying that DU level HRD parameters are presentand the HRD can be operated at the AU level or the DU level. Further,the du_hrd_params_present_flag can be set to zero when specifying thatDU level HRD parameters are not present and the HRD operates at the AUlevel.

The current SEI message may also include adu_cpb_params_in_pic_timing_sei_flag that specifies whether DU level CPBremoval delay parameters are present in a PT SEI message. Thedu_cpb_params_in_pic_timing_sei_flag may further specify whether DUlevel CPB removal delay parameters are present in a DUI SEI message. Ina specific example, the du_cpb_params_in_pic_timing_sei_flag can be setto one when specifying that that DU level CPB removal delay parametersare present in a PT SEI message and no DUI SEI message is available.Further, the du_cpb_params_in_pic_timing_sei_flag can be set to zerowhen specifying that DU level CPB removal delay parameters are presentin a DUI SEI message and PT SEI messages do not include DU level CPBremoval delay parameters.

In an embodiment, the video decoder expects a du_hrd_params_present_flagand a du_cpb_params_in_pic_timing_sei_flag to indicate the presenceand/or location of DU level parameters as described above based on VVCor some other standard. If, however, the decoder determines that thiscondition is not true, the decoder may detect an error, signal an error,request that a revised bitstream (or a portion thereof) be resent, ortake some other corrective measures to ensure that a conformingbitstream is received.

At step 1003, the decoder can decode the coded picture from the VCL NALunits to produce a decoded picture. For example, the decoder candetermine that the bitstream has been checked for conformance tostandards based on the presence of the current SEI message. Accordingly,the decoder can determine that the bitstream is decodable based on thepresence of the current SEI message. It should be noted that, in somecases, the OLS received at the decoder may contain a single layer. Insuch cases, the layer/OLS may not include a VPS. Due to the presence ofthe du_hrd_params_present_flag and thedu_cpb_params_in_pic_timing_sei_flag, the current SEI message does notdepend on the VPS. As such, the lack of VPS does not cause errors whencurrent SEI message is parsed. At step 1005, the decoder can forward thedecoded picture for display as part of a decoded video sequence.

FIG. 11 is a schematic diagram of an example system 1100 for coding avideo sequence using a bitstream that employs a SEI message that may notdepend on a VPS. System 1100 may be implemented by an encoder and adecoder such as a codec system 200, an encoder 300, a decoder 400,and/or a video coding device 800. Further, the system 1100 may employ aHRD 500 to perform conformance tests on a multi-layer video sequence 600and/or a bitstream 700. In addition, system 1100 may be employed whenimplementing method 100, 900, and/or 1000.

The system 1100 includes a video encoder 1102. The video encoder 1102comprises an encoding module 1103 for encoding a coded picture into abitstream. The encoding module 1103 is further for encoding into thebitstream a current SEI message that comprises adu_hrd_params_present_flag that specifies whether DU level HRDparameters are present in the bitstream. The video encoder 1102 furthercomprises a HRD module 1105 for performing a set of bitstreamconformance tests on the bitstream based on the current SEI message. Thevideo encoder 1102 further comprises a storing module 1106 for storingthe bitstream for communication toward a decoder. The video encoder 1102further comprises a transmitting module 1107 for transmitting thebitstream toward a video decoder 1110. The video encoder 1102 may befurther configured to perform any of the steps of method 900.

The system 1100 also includes a video decoder 1110. The video decoder1110 comprises a receiving module 1111 for receiving a bitstreamcomprising a coded picture and a current SEI message that comprises adu_hrd_params_present_flag that specifies whether DU level HRDparameters are present in the bitstream. The video decoder 1110 furthercomprises a decoding module 1113 for decoding the coded picture toproduce a decoded picture. The video decoder 1110 further comprises aforwarding module 1115 for forwarding the decoded picture for display aspart of a decoded video sequence. The video decoder 1110 may be furtherconfigured to perform any of the steps of method 1000.

A first component is directly coupled to a second component when thereare no intervening components, except for a line, a trace, or anothermedium between the first component and the second component. The firstcomponent is indirectly coupled to the second component when there areintervening components other than a line, a trace, or another mediumbetween the first component and the second component. The term “coupled”and its variants include both directly coupled and indirectly coupled.The use of the term “about” means a range including ±10% of thesubsequent number unless otherwise stated.

It should also be understood that the steps of the exemplary methods setforth herein are not necessarily required to be performed in the orderdescribed, and the order of the steps of such methods should beunderstood to be merely exemplary. Likewise, additional steps may beincluded in such methods, and certain steps may be omitted or combined,in methods consistent with various embodiments of the presentdisclosure.

While several embodiments have been provided in the present disclosure,it may be understood that the disclosed systems and methods might beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, components, techniques, ormethods without departing from the scope of the present disclosure.Other examples of changes, substitutions, and alterations areascertainable by one skilled in the art and may be made withoutdeparting from the spirit and scope disclosed herein.

What is claimed is:
 1. A method implemented by a decoder, the methodcomprising: receiving, by a receiver of the decoder, a bitstreamcomprising a coded picture and a current supplemental enhancementinformation (SEI) message that comprises a decoding unit (DU)hypothetical reference decoder (HRD) parameters present flag(du_hrd_params_present_flag) that specifies whether DU level HRDparameters are present in the bitstream; and decoding, by a processor ofthe decoder, the coded picture to produce a decoded picture.
 2. Themethod of claim 1, wherein the du_hrd_params_present_flag furtherspecifies an HRD can be operated at an access unit (AU) level or a DUlevel.
 3. The method of claim 2, wherein the du_hrd_params_present_flagis set to one when specifying that the DU level HRD parameters arepresent and the HRD can be operated at the AU level or the DU level, andwherein the du_hrd_params_present_flag is set to zero when specifyingthat the DU level HRD parameters are not present and the HRD operates atthe AU level.
 4. The method of claim 1, wherein the current SEI messagefurther comprises a DU coded picture buffer (CPB) parameters in picturetiming (PT) SEI flag (du_cpb_params_in_pic_timing_sei_flag) thatspecifies whether DU level CPB removal delay parameters are present in aPT SEI message.
 5. The method of claim 4, wherein thedu_cpb_params_in_pic_timing_sei_flag further specifies whether the DUlevel CPB removal delay parameters are present in a decoding unitinformation (DUI) SEI message.
 6. The method of claim 4, wherein thedu_cpb_params_in_pic_timing_sei_flag is set to one when specifying thatthat the DU level CPB removal delay parameters are present in a PT SEImessage and no DUI SEI message is available, and wherein thedu_cpb_params_in_pic_timing_sei_flag is set to zero when specifying thatthe DU level CPB removal delay parameters are present in a DUI SEImessage and PT SEI messages do not include the DU level CPB removaldelay parameters.
 7. The method of claim 1, wherein the current SEImessage is a Buffering Period (BP) SEI message, a picture timing (PT)SEI message, or a decoding unit information (DUI) SEI message.
 8. Amethod implemented by an encoder, the method comprising: encoding, by aprocessor of the encoder, a coded picture into a bitstream; encodinginto the bitstream, by the processor, a current supplemental enhancementinformation (SEI) message that comprises a decoding unit (DU)hypothetical reference decoder (HRD) parameters present flag(du_hrd_params_present_flag) that specifies whether DU level HRDparameters are present in the bitstream; performing, by the processor, aset of bitstream conformance tests on the bitstream based on the currentSEI message; and storing, by a memory coupled to the processor, thebitstream for communication toward a decoder.
 9. The method of claim 8,wherein the du_hrd_params_present_flag further specifies an HRD can beoperated at an access unit (AU) level or a DU level.
 10. The method ofclaim 9, wherein the du_hrd_params_present_flag is set to one whenspecifying that the DU level HRD parameters are present and the HRD canbe operated at the AU level or the DU level, and wherein thedu_hrd_params_present_flag is set to zero when specifying that the DUlevel HRD parameters are not present and the HRD operates at the AUlevel.
 11. The method of claim 8, wherein the current SEI messagefurther comprises a DU coded picture buffer (CPB) parameters in picturetiming (PT) SEI flag (du_cpb_params_in_pic_timing_sei_flag) thatspecifies whether DU level CPB removal delay parameters are present in aPT SEI message.
 12. The method of claim 11, wherein thedu_cpb_params_in_pic_timing_sei_flag further specifies whether the DUlevel CPB removal delay parameters are present in a decoding unitinformation (DUI) SEI message.
 13. The method of claim 11, wherein thedu_cpb_params_in_pic_timing_sei_flag is set to one when specifying thatthat the DU level CPB removal delay parameters are present in a PT SEImessage and no decoding unit information (DUI) SEI message is available,and wherein the du_cpb_params_in_pic_timing_sei_flag is set to zero whenspecifying that the DU level CPB removal delay parameters are present ina DUI SEI message and PT SEI messages do not include the DU level CPBremoval delay parameters.
 14. The method of claim 8, wherein the currentSEI message is a Buffering Period (BP) SEI message, a picture timing(PT) SEI message, or a decoding unit information (DUI) SEI message. 15.A video coding device comprising: a receiver configured to receive abitstream comprising a coded picture and a current supplementalenhancement information (SEI) message that comprises a decoding unit(DU) hypothetical reference decoder (HRD) parameters present flag(du_hrd_params_present_flag) that specifies whether DU level HRDparameters are present in the bitstream; and a processor coupled to thereceiver and configured to decode the coded picture to produce a decodedpicture.
 16. The video coding device of claim 15, wherein thedu_hrd_params_present_flag further specifies an HRD can be operated atan access unit (AU) level or a DU level.
 17. The video coding device ofclaim 16, wherein the du_hrd_params_present_flag is set to one whenspecifying that DU level HRD parameters are present and the HRD can beoperated at the AU level or the DU level, and wherein thedu_hrd_params_present_flag is set to zero when specifying that the DUlevel HRD parameters are not present and the HRD operates at the AUlevel.
 18. The video coding device of claim 15, wherein the current SEImessage further comprises a DU coded picture buffer (CPB) parameters inpicture timing (PT) SEI flag (du_cpb_params_in_pic_timing_sei_flag) thatspecifies whether the DU level CPB removal delay parameters are presentin a PT SEI message.
 19. The video coding device of claim 18, whereinthe du_cpb_params_in_pic_timing_sei_flag further specifies whether theDU level CPB removal delay parameters are present in a decoding unitinformation (DUI) SEI message.
 20. The video coding device of claim 18,wherein the du_cpb_params_in_pic_timing_sei_flag is set to one whenspecifying that that the DU level CPB removal delay parameters arepresent in a PT SEI message and no decoding unit information (DUI) SEImessage is available, and wherein thedu_cpb_params_in_pic_timing_sei_flag is set to zero when specifying thatthe DU level CPB removal delay parameters are present in a DUI SEImessage and PT SEI messages do not include the DU level CPB removaldelay parameters.